Thalassemia is a group of inherited hemoglobin disorders characterized by reduced or absent synthesis of one or more globin chains, leading to ineffective erythropoiesis and microcytic hypochromic anemia.

Exam domain	One-glance essentials
Definition / diagnosis	*Inherited quantitative reduction in globin-chain synthesis*, unlike qualitative haemoglobinopathies ^[1] Chain imbalance causes ineffective erythropoiesis and haemolysis
Epidemiology / risks	*Highly prevalent in HK Chinese; total carrier rate ~11.3%* ^[2] Southeast Asian cis α-globin deletion means two carrier parents risk Hb Bart's hydrops fetalis ^[3]
Core mechanism	α-thalassaemia: excess β chains → HbH (β₄); fetal excess γ chains → Hb Bart's (γ₄) ^[2] β-thalassaemia: insoluble excess α chains precipitate → intramedullary death + splenic haemolysis
Clinical picture	Trait: asymptomatic microcytosis disproportionate to anaemia with relatively high RBC count ^[2] β-thal major presents after the *3–6 month HbF→HbA switch*; severe disease causes jaundice, splenomegaly, marrow expansion and growth failure ^[2]
Investigations	CBC/film: microcytosis, hypochromia, target cells ± basophilic stippling; iron studies usually normal ^[2] *HbA₂ ≥ 3.5% supports β-thal trait; HbH identifies α-thal intermedia* ^[2] Normal Hb study does not exclude α-thal trait → confirm by DNA analysis
Management	Trait: reassurance + genetic counselling; *no iron unless deficiency is proven* ^[2] TDT: regular leukodepleted, extended-matched transfusions + iron chelation ^[4] Allogeneic HSCT is potentially curative in selected severe disease
Complications	*Iron overload* → cardiomyopathy, cirrhosis and endocrine failure; monitor liver/heart MRI T2* ^[4] Chronic haemolysis/marrow expansion → pigment stones, skeletal deformity and extramedullary haematopoiesis
Prevention / follow-up	*Carrier detection → genetic counselling → prenatal genotyping*: 'for the patient, carrier and unborn' ^[2]^[3] If both partners carry a severe compatible genotype, offer CVS/amniocentesis with molecular testing ^[3]
Exam traps	Do not label every microcytosis IDA: thal trait has normal iron and normal/↑ RBC count ^[2] Iron deficiency can lower HbA₂ and mask β-thal trait—replete iron, then repeat study HbA1c is unreliable when RBC survival or haemoglobin composition is abnormal

References

^[1] Lecture slides: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (disorders of haemoglobin) ^[2] Senior notes: Block A - Many members of the family have anaemia.pdf (epidemiology, clinical syndromes and laboratory diagnosis) ^[3] Lecture slides: GC 113. Can we get married Pre-marital, pre-pregnancy and pre-natal counselling.pdf ^[4] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (iron overload, MRI T2* and chelation)

Thalassemia

Thalassemia (from Greek: thalassa = sea, referring to the Mediterranean Sea; haima = blood) is a group of inherited disorders of haemoglobin characterised by a reduced rate of synthesis of one or more of the globin chains ^[1]^[2]. This is fundamentally a quantitative defect — the globin chains produced are structurally normal, but there simply aren't enough of them. This contrasts with haemoglobinopathies (e.g. sickle cell disease / HbS), which are qualitative defects — structurally abnormal haemoglobin ^[1].

Key Distinction — Thalassemia vs Haemoglobinopathy

Thalassemia = reduced rate of synthesis of normal globin chains (quantitative defect)
Haemoglobinopathy = structurally abnormal globin chain (qualitative defect, e.g. HbS)
Some variants straddle both categories: thalassemic haemoglobinopathies (e.g. Hb E, Hb Constant Spring) produce a structurally abnormal chain that is also synthesised at a reduced rate ^[1].

The consequence of reduced globin chain synthesis is an imbalanced α-to-β chain ratio. The excess unpaired chains are unstable, precipitate within red cell precursors and mature red cells, causing ineffective erythropoiesis and haemolysis — the two cardinal pathological processes of thalassemia ^[3]^[4].

2. Epidemiology

Most common single-gene (monogenic) disorder worldwide ^[3]^[4].
The "thalassemia belt" stretches across the Mediterranean, Middle East, Indian subcontinent, and Southeast Asia — overlapping precisely with historical and current malaria-endemic zones.
An estimated ~5% of the world's population carries a thalassemia or haemoglobinopathy gene.
WHO estimates ~60,000 severely affected children are born annually worldwide.

This is extremely relevant in Hong Kong because thalassemia is prevalent in HK Chinese ^[2]^[3]^[4]:

Carrier State	Prevalence in HK Chinese
α-thalassemia trait	~5% (among those with low MCV)
β-thalassemia trait	~3%
HbE trait	~0.3%
α-thal carrier (1 gene deleted, normal MCV)	~3%
Total carrier rate	~11.3%

^[2] "Adding everything together, 11.3% will be carriers" — This means roughly 1 in 9 people in Hong Kong carry some form of thalassemia gene. This has enormous implications for pre-marital and pre-natal counselling.

High Yield — HK Prevalence

In HK Chinese with low MCV: ~5% α-thal carrier, ~3% β-thal carrier, ~0.3% HbE. With normal MCV: ~3% α-thal (single gene deletion). Total carrier rate ~11.3%. This makes pre-marital screening and genetic counselling critical public health measures in Hong Kong ^[2]^[5].

Ethnicity: Southeast Asian (including Chinese), Mediterranean, Middle Eastern, South Asian, African descent
Family history: Autosomal recessive inheritance — both parents must be carriers for a child to be affected with thalassemia major/intermedia
Consanguinity: Increases risk of homozygous states
Geographic origin from the thalassemia belt

Why is the Thalassemia Gene So Common? — Malaria Selection Advantage

The thalassemia gene is maintained in the human population because it confers greater immunity in heterozygous individuals against malaria ^[3]^[4]. This is the classic example of heterozygote advantage (balanced polymorphism):

Plasmodium falciparum parasitises red blood cells. Thalassemic red cells have altered membrane properties, increased oxidative stress, and are more rapidly cleared by the spleen — making them a hostile environment for the parasite.
Heterozygous carriers (trait) have a survival advantage in malaria-endemic areas without the severe disease of homozygotes.
This is why the thalassemia belt geographically overlaps with historical malaria endemic zones.

4. Anatomy and Physiology of Normal Haemoglobin

Understanding thalassemia requires knowing how haemoglobin works from first principles.

Haemoglobin (Hb) is a tetramer — 4 globin chains, each carrying a haem group (containing Fe²⁺ that binds O₂). Normal adult Hb consists of:

Haemoglobin	Structure	Normal % in Adults
HbA	α₂β₂	~96–97%
HbA₂	α₂δ₂	~2–3.5%
HbF (foetal)	α₂γ₂	< 1% (elevated in neonates)

This is absolutely critical to understanding thalassemia:

α-globin genes: Located on chromosome 16. There are 4 copies (two on each chromosome 16) — designated αα/αα. Each chromosome 16 carries two α-globin genes in tandem (α2 and α1).
β-globin gene: Located on chromosome 11. There are 2 copies (one on each chromosome 11) — designated β/β.
The β-globin gene cluster on chromosome 11 also contains the ε (embryonic), γ (foetal), and δ genes, arranged 5′→3′ in the order of their developmental expression: ε → γ → δ → β.

This concept explains when different thalassemias become clinically manifest:

Embryonic life: ζ₂ε₂ (Hb Gower 1), α₂ε₂ (Hb Gower 2), ζ₂γ₂ (Hb Portland)
Foetal life: Predominantly HbF (α₂γ₂)
After birth: Gradual switch from γ-chain to β-chain production → transition from HbF to HbA, complete by 3–6 months of age

Why β-Thalassemia Major Presents at 3–6 Months, Not at Birth

Beta-thalassemia is not affected at birth — because at birth, haemoglobin is predominantly HbF (α₂γ₂), which does NOT require β-chains. The switch to adult β-haemoglobin occurs at 3–6 months of life. Once the body tries to switch to β-chain production and cannot produce sufficient β-chains, anaemia develops ^[2]. This is why β-thalassemia major presents with anaemia in the first year of life ^[2].

In contrast, α-thalassemia affects ALL haemoglobins at ALL stages (embryonic, foetal, and adult), because α-chains are required in every developmental haemoglobin. Therefore, severe α-thalassemia (Hb Bart's hydrops fetalis) presents in utero ^[2].

5. Etiology (Focus on Hong Kong)

Cause: Most commonly due to gene deletions (occasionally non-deletional point mutations) affecting the α-globin genes on chromosome 16.

Since there are 4 α-globin gene copies, the severity depends on how many are lost:

Genotype	# Genes Deleted	Clinical Syndrome
-α/αα	1	Silent carrier (α-thal minima)
--/αα or -α/-α	2	α-thalassemia trait (α-thal minor)
--/-α	3	HbH disease (α-thal intermedia)
--/--	4	Hb Bart's hydrops fetalis (α-thal major)

Important in HK: The most common α-thal deletion in Southeast Asians (including HK Chinese) is the Southeast Asian (SEA) deletion (--SEA), which deletes both α-genes on the same chromosome (cis deletion). This is clinically critical because:

Two parents with --SEA/αα (α-thal trait, cis type) can produce a child with --/-- (Hb Bart's hydrops fetalis — lethal)
In contrast, the trans deletion (-α/-α), common in Africans, cannot produce Hb Bart's because each chromosome still has one functional gene

Cis vs Trans Deletion — Why it Matters in HK

In Southeast Asians (including HK Chinese), the cis deletion (--/αα) is common. Two cis-trait parents have a 25% chance of having a child with Hb Bart's hydrops fetalis (--/--), which is lethal.

In Africans, the trans deletion (-α/-α) is common. Even if both parents are carriers, the worst outcome is HbH disease (--/-α), which is survivable. Hb Bart's essentially does not occur in African populations.

This is why pre-marital/prenatal genetic counselling is so important in Hong Kong ^[5].

Non-deletional α-thalassemia

Hb Constant Spring (HbCS) is the most common non-deletional α-thal variant in Southeast Asia ^[1].
It results from a mutation in the stop codon of the α2-globin gene → the ribosome reads through into the 3′ UTR → producing an elongated, unstable α-chain (172 amino acids instead of 141).
HbCS is synthesised at a very reduced rate → acts as a thalassemic haemoglobinopathy.
αCSα/αα = clinically silent carrier
--/αCSα = HbH/CS disease — tends to be more severe than standard HbH disease (--/-α)

Cause: Almost always due to point mutations (> 300 described) — NOT deletions (unlike α-thal). These mutations affect transcription, RNA processing, translation, or post-translational stability of the β-globin mRNA/protein.

Two types of mutations:

Mutation Type	Symbol	Meaning
β⁺	Some β-chain production	Reduced but not absent
β⁰	No β-chain production	Complete absence

Clinical severity depends on the combination:

Genotype	Clinical Syndrome
β⁰/β or β⁺/β	β-thalassemia trait (minor)
β⁺/β⁺	β-thalassemia intermedia (Cooley's)
β⁰/β⁰ or β⁰/β⁺	β-thalassemia major (Cooley's anaemia — transfusion dependent)

Common mutations in HK Chinese:

Codons 41/42 (-TTCT) — frameshift, β⁰
IVS-II-654 (C→T) — splicing defect, β⁺ (but severe)
Codon 17 (A→T) — nonsense, β⁰
-28 (A→G) — promoter, β⁺

Deletions involving both δ and β genes → compensatory ↑ HbF production
HPFH: More complete compensation → clinically milder
δβ-thal: Less complete compensation → resembles β-thal intermedia

6. Pathophysiology

This is the core of understanding thalassemia. Everything — the clinical features, the complications, the management — flows from understanding the pathophysiology.

Normally there is equal production of α- and β-chains ^[3]^[4]. In thalassemia:

α-thalassemia: Reduced α-chain → relative excess of β-chains (in adults) or γ-chains (in foetuses/neonates)
β-thalassemia: Reduced β-chain → relative excess of α-chains

The excess unpaired chains polymerise and precipitate out of solution in RBCs due to instability ^[3]^[4].

6.2 Consequences of Excess Unpaired Chains

Excess β-chains form β₄ tetramers = Haemoglobin H (HbH)
Excess γ-chains form γ₄ tetramers = Haemoglobin Bart's (Hb Bart's)
HbH (β₄) and Hb Bart's (γ₄) are non-functional Hb with very high O₂ affinity (left-shifted O₂-dissociation curve) which do not transport oxygen and result in chronic hypoxia and extravascular haemolysis ^[3]^[4]
HbH and Hb Bart's precipitate and form inclusion bodies in circulating red cells → chronic haemolysis ^[3]^[4]

Why can HbH and Hb Bart's form stable tetramers? Because β-chains and γ-chains are relatively soluble even when unpaired. They can form homotetramers that are somewhat stable (though still dysfunctional). This is in stark contrast to α-chains, which are highly insoluble when unpaired.

Free α-globin chains and α₄ tetramers are very unstable, damage the red cell membrane and shorten RBC survival ^[3]^[4]
Unlike β-chains, α-chains are highly insoluble and cannot form stable tetramers. Instead, they precipitate as monomers and aggregates within erythroid precursors.
These precipitates generate reactive oxygen species (ROS), causing oxidative damage to the red cell membrane.
This explains why β-thalassemia major tends to be more severe than HbH disease — unpaired α-chains are more toxic to red cells than unpaired β-chains.

6.3 The Two Cardinal Pathological Processes

Precipitation of globin chains in red cell precursors results in ineffective erythropoiesis — early destruction of RBC precursors in the bone marrow ^[3]^[4].

Erythroid precursors (especially in β-thal major) are damaged by precipitated α-chains and undergo apoptosis before they can be released as mature red cells.
The bone marrow is massively expanded (up to 25–30 times normal) in a futile attempt to compensate → this is the factory running on overdrive but producing defective products that get destroyed before leaving the factory.
Consequence: Despite enormous erythroid activity, very few functional red cells enter the circulation.

Those red cells that do manage to escape the bone marrow still contain inclusion bodies (precipitated chains, HbH, Hb Bart's).
These inclusions make the red cell rigid and damage the membrane → they are trapped and destroyed in the spleen (extravascular haemolysis).
This explains the characteristic splenomegaly in thalassemia.

The massively expanded but ineffective bone marrow drives a cascade of complications:

Bone marrow expansion → skeletal deformities (thalassemic facies, hair-on-end appearance on skull X-ray, pathological fractures)
Extramedullary haematopoiesis → hepatosplenomegaly, paravertebral masses
Increased intestinal iron absorption — the ineffective erythropoiesis drives suppression of hepcidin (the master regulator of iron homeostasis) via increased erythroferrone from the expanded erythroid marrow. Suppressed hepcidin → increased ferroportin expression on enterocytes and macrophages → increased iron absorption and release into plasma → iron overload even without transfusions (this is called non-transfusional iron overload).
Haemolysis → splenomegaly, jaundice, pigment gallstones

Iron overload in thalassemia comes from two sources:

Increased intestinal iron absorption (driven by ineffective erythropoiesis via hepcidin suppression)
Repeated blood transfusions (each unit of packed RBC contains ~200–250 mg iron, and the body does not have a good mechanism of iron excretion ^[6])

Iron overload is the leading cause of death in transfusion-dependent thalassemia if untreated. Iron deposits in:

Heart → cardiomyopathy, arrhythmias, heart failure (the most common cause of death)
Liver → fibrosis, cirrhosis
Endocrine glands → diabetes mellitus, hypogonadism, hypothyroidism, hypoparathyroidism, growth failure
Skin → bronze discolouration

7. Classification

Type	Chain Affected	Gene Location	Common Mutation Type
α-thalassemia	α-chain	Chromosome 16	Deletions (usually)
β-thalassemia	β-chain	Chromosome 11	Point mutations (usually)
δβ-thalassemia	δ and β chains	Chromosome 11	Deletions
εγδβ-thalassemia	All β-cluster genes	Chromosome 11	Large deletions

This is the most important classification for clinical practice and exams ^[2]:

Clinical Syndrome	α-Thalassemia	β-Thalassemia
Thalassemia major (transfusion-dependent)	All 4 α genes deleted → Hb Bart's hydrops fetalis	Both β genes mutated: β⁰/β⁰ or β⁰/β⁺
Thalassemia intermedia (moderate anaemia, not routinely transfusion-dependent)	3 α genes deleted → HbH disease	Both β genes mutated: β⁺/β⁺
Thalassemia trait / minor (mild/no anaemia)	1 or 2 α genes deleted	1 β gene mutated: either β⁰ or β⁺
Silent carrier	1 α gene deleted (-α/αα)	—

Cooley's Anaemia

Cooley's anaemia is the eponymous name for β-thalassemia major, named after Thomas Cooley who described it in 1925. The senior notes mention this term for both β-thal major and intermedia in different contexts ^[2]. For exams, Cooley's anaemia = β-thal major (transfusion-dependent).

Current guidelines (TIF / Thalassemia International Federation, 2024) increasingly use a functional classification:

Category	Includes
Transfusion-Dependent Thalassemia (TDT)	β-thal major, severe HbE/β-thal, Hb Bart's survivors
Non-Transfusion-Dependent Thalassemia (NTDT)	β-thal intermedia, HbH disease, mild HbE/β-thal

This is more clinically useful because it determines management — the key question is: does this patient need regular transfusions or not?

8. Clinical Features

8.1 Organisation by Syndrome Severity

Symptoms: Mild to no anaemia (Hb 10–13 g/dL) ^[2]

Usually asymptomatic — discovered incidentally on CBC showing microcytosis with relatively preserved Hb
May have mild fatigue during physiological stress (pregnancy, infection)

Signs:

Usually no splenomegaly ^[2]
Mild to no jaundice ^[2]
Only show microcytosis on blood film ^[2]

Pathophysiological basis: Only one (β-thal) or 1–2 (α-thal) genes are affected → sufficient globin chain production to maintain near-normal Hb. The slight chain imbalance causes ineffective erythropoiesis at a subclinical level, producing microcytic cells but not enough to cause significant anaemia.

When the anaemia is more severe than what one expects from the thalassemia, investigations for other causes of anaemia are necessary ^[2]. For example, a thalassemia trait patient suddenly presenting with Hb 4 g/dL → impossible from trait alone → look for concomitant iron deficiency, bleeding, etc.

Symptoms:

Moderate degree of anaemia (Hb 6–10 g/dL) ^[2]
Fatigue, exercise intolerance
Episodic worsening during infections (HbH disease is characterised by acute haemolytic crises precipitated by infections, fever, oxidant drugs — similar concept to G6PD)

Signs:

Mild jaundice ^[2] — due to chronic low-grade haemolysis → unconjugated hyperbilirubinaemia
Mild to moderate splenomegaly ^[2] — the spleen is working overtime destroying abnormal red cells
Mild skeletal changes (less severe than major)
Do not require lifelong transfusion ^[2] — but may need occasional transfusions during crises or pregnancy

Pathophysiological basis: In HbH disease (--/-α), the majority of Hb is normal HbA, but a significant proportion (~5–30%) is HbH (β₄) which is unstable and has very high O₂ affinity → cannot deliver O₂ effectively. The HbH precipitates in red cells forming inclusion bodies → extravascular haemolysis in the spleen.

This is the full-blown clinical picture — the "classic" thalassemia presentation.

Age of Presentation: Not affected at birth → anaemia in the first year of life (typically 3–6 months) ^[2], because this is when the γ→β haemoglobin switch occurs. Parents notice the baby becoming progressively pale, irritable, and failing to thrive.

Symptoms:

Symptom	Pathophysiological Basis
Progressive pallor	Severe anaemia (Hb can drop to 3–4 g/dL without transfusion) from ineffective erythropoiesis + haemolysis
Irritability, lethargy	Tissue hypoxia from severe anaemia
Poor feeding, failure to thrive	Chronic anaemia → ↓ oxygen delivery → poor growth; also chronic illness and metabolic demands of massive erythropoiesis
Recurrent infections	Iron overload impairs immune function; also functional hyposplenism later
Abdominal distension	Massive hepatosplenomegaly (extramedullary haematopoiesis + haemolysis + iron deposition)

Signs:

Sign	Pathophysiological Basis
Thalassemic facies (frontal bossing, malar prominence, maxillary hypertrophy, dental malocclusion, flat nasal bridge)	Massive bone marrow expansion in the skull and facial bones. The marrow cavity expands outward → "chipmunk facies". The diploic space widens, causing the classic "hair-on-end" / "crew-cut" appearance on skull X-ray.
Hepatosplenomegaly	Extramedullary haematopoiesis: The overwhelmed bone marrow recruits the liver and spleen (foetal haematopoietic sites) to help produce red cells. Haemolysis: The spleen traps and destroys abnormal red cells. Iron overposition: Iron deposits in liver parenchyma.
Jaundice	Chronic haemolysis → ↑ unconjugated bilirubin
Pallor	Severe anaemia
Growth retardation, short stature	Chronic anaemia + iron overload damaging the pituitary/growth hormone axis + high metabolic demands of expanded erythropoiesis
Delayed puberty / hypogonadism	Iron deposition in the pituitary and gonads
Bronze skin pigmentation	Iron deposition in the skin (haemosiderosis)
Gallstones	Chronic haemolysis → excess bilirubin → pigment (black) gallstones
Leg ulcers	Chronic tissue hypoxia + endothelial dysfunction (more common in intermedia/NTDT than major)
Osteopenia / pathological fractures	Bone marrow expansion thins cortical bone; iron overload damages osteoblasts; hypogonadism and other endocrinopathies contribute
Cardiac findings (later)	Iron-overload cardiomyopathy → displaced apex beat, S3 gallop, signs of heart failure; arrhythmias

Clinical Features — Stigmata of Chronic Haemolysis

Signs and symptoms of chronic haemolysis include: Hepatomegaly, Splenomegaly, Osteopenia, Gallstones, Premature biliary tract disease, Leg ulcers ^[3]^[4].

Laboratory findings of chronic haemolysis: Indirect (unconjugated) hyperbilirubinaemia, ↑ LDH, ↓ Haptoglobin ^[3]^[4].

Clinical Features:

Dies in utero or shortly after birth ^[2]
The foetus has virtually no functional haemoglobin — all Hb is Hb Bart's (γ₄) which has very very high affinity for oxygen, cannot deliver oxygen to tissues ^[2]
Hydrops fetalis: Massive oedema, ascites, pleural/pericardial effusions — due to severe anaemia → high-output cardiac failure → increased capillary permeability
Massive hepatosplenomegaly (extramedullary haematopoiesis)
Placenta is large and oedematous
Maternal complications: Pre-eclampsia (toxaemia of pregnancy), obstructed labour due to large hydropic foetus, post-partum haemorrhage

May survive if active measures are taken (intrauterine transfusion), and will be transfusion dependent for life ^[2]. Modern centres have reported survival with intrauterine transfusions followed by stem cell transplant, but outcomes remain guarded.

Symptom/Sign	Mechanism
Pallor	↓ Hb from ineffective erythropoiesis + haemolysis
Jaundice	↑ unconjugated bilirubin from haemolysis
Splenomegaly	Extravascular haemolysis + extramedullary haematopoiesis
Hepatomegaly	Extramedullary haematopoiesis + iron deposition
Thalassemic facies	Marrow expansion in flat bones of skull/face
Gallstones (pigment)	Chronic haemolysis → ↑ bilirubin → precipitation
Growth failure / delayed puberty	Iron overload → pituitary/gonadal damage; chronic anaemia
Heart failure	Iron overload cardiomyopathy (most common cause of death in TDT)
Bronze skin	Dermal iron deposition
Leg ulcers	Tissue hypoxia + endothelial dysfunction
Osteopenia/fractures	Marrow expansion + iron toxicity to bone + endocrinopathy

This is a very common exam question because both present with hypochromic microcytic anaemia ^[2].

Red cell indices can help differentiate between thalassemia trait and iron deficiency — but red cell indices cannot differentiate between severe thalassemia and iron deficiency anaemia ^[2].

Parameter	Thalassemia Trait	Iron Deficiency Anaemia
Hb	Normal or slightly low	Can be very low (2–3 g/dL)
RBC count	High (↑)	Low (↓)
MCV	Low	Low
RDW	Normal (uniform microcytes)	High (anisocytosis)
Iron studies	Normal	↓ Ferritin, ↓ serum iron, ↑ TIBC
HbA₂	↑ in β-thal trait	Normal or ↓
Mentzer index (MCV/RBC)	< 13 (thalassemia)	> 13 (iron deficiency)

The key insight: In thalassemia trait, the red cells are small (low MCV) but the marrow is working fine and producing many red cells (high RBC count). In iron deficiency, the marrow wants to produce red cells but lacks raw material → fewer, smaller cells.

In our locality, the most common cause of hypochromic microcytic anaemia is still iron deficiency anaemia. But don't forget about thalassemia. ^[2]

Thalassemia and HbA1c

Thalassemia causes variable effects on HbA1c due to altered red cell lifespan (excess haemolysis → shorter RBC survival → falsely low HbA1c). This means HbA1c is unreliable in thalassemia patients for monitoring diabetes ^[7]. Alternative monitoring: fructosamine, glycated albumin, or continuous glucose monitoring.

9. Special Considerations

Three indications for performing a haemoglobin study ^[2]:

Differential diagnosis of anaemia in patients to ensure proper treatment
Detection of carrier state in order to provide genetic counselling — "Carrier mild, but if two carriers are married, need to have these conversations"
Genotyping in prenatal diagnosis

"For the patient, for the carrier, for the unborn" ^[2]

Pre-marital screening is recommended in Hong Kong given the high carrier rate (~11.3%). If both partners are carriers:

Both α-thal trait (cis type): 25% risk of Hb Bart's hydrops fetalis
Both β-thal trait: 25% risk of β-thal major
One α-thal trait + one β-thal trait: Generally no risk of severe disease (different genes affected)

Prenatal diagnosis can be performed by chorionic villus sampling (CVS) at 10–12 weeks or amniocentesis at 15–18 weeks, with molecular/DNA analysis ^[5].

In HK and Southeast Asia, HbH/CS disease (--/αCSα) is clinically more severe than standard deletional HbH disease (--/-α). These patients tend to have:

Lower baseline Hb
More severe haemolytic crises
Greater splenomegaly
More often require transfusions (some becoming transfusion-dependent)

HbE/β-thalassemia is the most common severe thalassemia syndrome globally (predominantly in Southeast Asia):

HbE (β²⁶ Glu→Lys) is a thalassemic haemoglobinopathy — produces a mildly abnormal β-chain at a reduced rate
When co-inherited with β-thal trait → variable severity from thal intermedia to thal major
Very important in Hong Kong given the ~0.3% HbE carrier rate ^[2]

MRI T2 of the liver and heart — non-invasive and accurate* ^[8] for monitoring iron overload, replacing:

Liver biopsy (too invasive, no longer used routinely)
Serum ferritin (too many confounding factors — infection, inflammation, liver disease — but still used as a screening/trending tool)

Iron chelation for treatment of iron overload ^[6]^[8]:

3 types: 1 is subcutaneous/IV, 2 are oral ^[8]
- Desferrioxamine (DFO) — SC/IV infusion (8–12 hours, 5–7 days/week). The oldest and most established chelator.
- Deferiprone (DFP/L1) — Oral, TDS. Particularly effective for cardiac iron removal.
- Deferasirox (DFX) — Oral, once daily. Most convenient, now first-line in many centres.

High Yield Summary

Definition: Thalassemia = reduced rate of synthesis of globin chains (quantitative defect), NOT structural abnormality.
Epidemiology: Most common single-gene disorder worldwide. In HK: α-thal trait ~5%, β-thal trait ~3%, total carrier rate ~11.3%. Maintained by heterozygote advantage against malaria.
Genetics: α-globin = 4 gene copies (chr 16), β-globin = 2 gene copies (chr 11). α-thal usually deletions; β-thal usually point mutations. SEA deletion (cis) in HK = risk of Hb Bart's hydrops fetalis.
Pathophysiology: Globin chain imbalance → excess unpaired chains precipitate → (a) ineffective erythropoiesis (destruction in marrow) + (b) haemolysis (peripheral destruction in spleen). Unpaired α-chains (in β-thal) are MORE toxic than unpaired β-chains (in α-thal).
Iron overload from ↑ gut absorption (hepcidin suppression by erythroferrone) + transfusions. Heart is the #1 cause of death. Monitor with MRI T2*. Treat with chelation (DFO/DFP/DFX).
Clinical Classification: Major (transfusion-dependent) → Intermedia (moderate, not routinely transfusion-dependent) → Trait (mild/asymptomatic).
β-thal major presents at 3–6 months (after γ→β switch); Hb Bart's presents in utero (α-chains needed at all stages).
Thal trait vs IDA: Both microcytic. Thal trait = high RBC count, normal/mild ↓ Hb, normal iron studies. IDA = low RBC count, can be very low Hb, abnormal iron studies.
Pre-marital/prenatal counselling is critical in HK given high carrier rate. Three indications for Hb study: for the patient, for the carrier, for the unborn.
Thalassemia causes variable effects on HbA1c — unreliable for DM monitoring.

Active Recall - Thalassemia (Definition to Clinical Features)

^[1] Lecture slides: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (Disorders of Hemoglobin section) ^[2] Senior notes: Block A - Many members of the family have anaemia.pdf (Clinical syndromes, epidemiology, laboratory diagnosis sections) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Thalassemia section — epidemiology, pathogenesis, clinical manifestations) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Thalassemia section — epidemiology, pathogenesis, clinical manifestations) ^[5] Lecture slides: GC 113. Can we get married Pre-marital, pre-pregnancy and pre-natal counselling.pdf; Block C - Can we get married_ Pre-marital, pre-pregnancy and prenatal counselling.pdf ^[6] Senior notes: Block A - Hematology Interactive Tutorial.pdf (Iron overload and chelation section) ^[7] Senior notes: Block A - Polyuria and polydipsia_ glucose metabolism; diabetes mellitus; diabetic ketoacidosis.pdf (HbA1c limitations section) ^[8] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (Transfusion haemosiderosis monitoring and treatment)

Differential Diagnosis of Thalassemia

When you encounter a patient with suspected thalassemia, you're usually working through one (or both) of two clinical scenarios:

Incidental finding of hypochromic microcytic anaemia on CBC — "Is this thalassemia or something else causing the low MCV?"
A patient with features of chronic haemolysis (pallor, jaundice, splenomegaly) — "What's the cause of the haemolysis?"

The differential diagnosis therefore needs to cover both the MCV-based approach (microcytic anaemia DDx) and the haemolysis-based approach (haemolytic anaemia DDx), since thalassemia sits at the intersection of both.

This is the most common exam scenario: a CBC shows hypochromic microcytic anaemia — what's your differential?

GC High Yield — Two Most Common Causes of Microcytic Anaemia in HK

In Hong Kong, the two most common causes of hypochromic microcytic anaemia are: (1) Iron deficiency anaemia, and (2) Thalassemia ^[9]. Both are extremely prevalent locally.

Triggers for laboratory diagnosis of thalassemia: Low MCV +/- clinical features (pallor, splenomegaly, failure to thrive) ^[10]^[11].

The full differential for microcytic anaemia can be remembered with the mnemonic "TAILS":

Cause	Mechanism (Why Microcytic?)	Key Distinguishing Features
Thalassemia	Reduced globin chain synthesis → less Hb per cell → cells divide extra times to "try to concentrate" Hb → smaller cells	High RBC count, low-normal RDW, target cells, basophilic stippling, +ve Hb study
Anaemia of chronic disease (ACD)	Hepcidin-mediated iron sequestration → functional iron deficiency. Usually normocytic, but can be mildly microcytic in ~20-30%	Usually normocytic; low serum iron BUT low TIBC and normal/↑ ferritin (cf. IDA where TIBC is high)
Iron deficiency anaemia (IDA)	Insufficient iron for haem synthesis → ↓ Hb production → microcytosis	Low ferritin, low serum iron, ↑ TIBC ^[12], pencil cells/elliptocytes, high RDW, reactive thrombocytosis
Lead poisoning	Lead inhibits δ-aminolevulinic acid dehydratase and ferrochelatase → impaired haem synthesis	Basophilic stippling (coarse), abdominal pain, lead lines on gingiva, occupational/environmental exposure
Sideroblastic anaemia	Defective haem synthesis in mitochondria → iron accumulates in mitochondria forming "ringed sideroblasts"	Dimorphic blood film, ringed sideroblasts on BM, can be hereditary or acquired (MDS) ^[12]

Sideroblastic anaemia: think of MDS, but very rare (and frank MDS would be macrocytic) ^[12].

Key Table: Thalassemia Trait vs Iron Deficiency Anaemia

This is a very commonly examined distinction ^[2]^[9]^[10].

Parameter	Thalassemia Trait	Iron Deficiency Anaemia
Haemoglobin	10–13 g/dL (normal or slightly low)	Any level — can be very low (2–3 g/dL)
RBC count	Normal or increased	Decreased
MCV	↓ but usually not < 65 fL	Any level
Serum iron	Normal	Decreased
TIBC	Normal	Increased
% iron saturation / transferrin saturation	Normal	Decreased
Serum ferritin	Normal	Decreased
RDW	Normal or slightly high	Can be very high
HbA₂	↑ (in β-thal trait)	Normal or ↓
Blood smear	Microcytic, uniform, target cells	Non-uniform size, pencil cells

Two methods to distinguish thalassemia trait from IDA, proposed by different lecturers ^[9]^[13]:

Sin says: RDW → higher suggests IDA (greater variation in RBC size), lower suggests thalassemia (genetic defect → all RBCs microcytic to a similar extent, so RDW generally normal) ^[9]^[13]

Hwang says: RBC count → thalassemia marrow is fine, can compensate to create more RBCs, albeit with lower Hb within them. IDA marrow lacks raw material → fewer cells ^[9]^[13]

"Interpret as a whole" ^[13]

Peripheral Blood Smear — The King

"Blood smear is king — can clearly differentiate based on features" ^[13]:

β-thalassemia trait: microcytic with target cells, uniform cell size
Iron deficiency anaemia: non-uniform size (anisocytosis), pencil cells (elliptocytes)

Additional thalassemia smear features: anisocytosis and poikilocytosis, target cells, spherocytes, schistocytes, basophilic stippling ^[9]. The basophilic stippling is the major feature distinguishing the two ^[9].

Don't Forget Co-existing Conditions

When the anaemia is more severe than what one expects from the thalassemia, investigations for other causes of anaemia are necessary ^[2]. A thalassemia trait patient presenting with Hb 4 g/dL cannot be explained by trait alone — look for concurrent IDA, GI bleeding, infection, or another cause. Thalassemia trait patients can also develop iron deficiency (e.g. from menorrhagia or poor diet), and when this happens, HbA₂ may be falsely normalised (iron deficiency suppresses δ-chain synthesis), making β-thal trait harder to detect. Always correct iron deficiency first, then recheck HbA₂.

When thalassemia presents with features of haemolysis (pallor, jaundice, splenomegaly, ↑ LDH, ↑ unconjugated bilirubin, ↓ haptoglobin), you need to consider the broader differential of haemolytic anaemia.

Key haemolytic anaemia laboratory features ^[14]:

Anaemia (mildly macrocytic usually) with reticulocytosis
Increase in unconjugated bilirubin, LDH
Reduced serum haptoglobin
Increased methaemalbumen
Blood film: polychromasia; spherocytes (HS, AIHA); RBC fragmentation (MAHA); RBC agglutination (cold agglutinin disease)
Direct antiglobulin test — positive in immune haemolytic anaemia

A Note on Reticulocyte Count in Thalassemia

In most haemolytic anaemias, you expect a compensatory reticulocytosis (marrow ramps up production). However, in thalassemia — especially β-thalassemia major — the reticulocyte count is RELATIVELY ↓ (inappropriately low, commonly < 8%) when compared to the degree of anaemia. Why? Because the dominant process is ineffective erythropoiesis — the precursors die in the marrow before they can become reticulocytes ^[3]^[4]. This is a crucial distinguishing feature from other haemolytic anaemias where the marrow is functioning normally.

Intramedullary haemolysis DDx: pernicious anaemia, thalassemia major, MDS ^[12].

Classification: Inherited vs Acquired; Intrinsic vs Extrinsic

Inherited haemolytic anaemias — think in terms of the three components of the RBC ^[1]:

RBC Component	Disorder	Key Features to Distinguish from Thalassemia
Membrane	Hereditary spherocytosis (HS)	Autosomal dominant; spherocytes on smear (not target cells); +ve osmotic fragility test; MCHC ↑; Northern European ancestry more common
	Hereditary elliptocytosis (HE)	Elliptocytes on smear; usually milder
Metabolism (enzyme)	G6PD deficiency	X-linked; episodic haemolysis triggered by infection/oxidants/fava beans; bite cells and Heinz bodies during crisis; normal baseline between crises (no chronic anaemia in most variants)
	Pyruvate kinase deficiency	AR; chronic haemolysis (not episodic); echinocytes on smear
Haemoglobin	Thalassemia	Quantitative defect — microcytic, target cells, low MCV
	Haemoglobinopathy (e.g. HbS, HbC, HbE)	Qualitative defect — sickle cells (HbS), target cells (HbC/E); Hb electrophoresis diagnostic
	Unstable haemoglobins	Rare; Heinz bodies; heat/isopropanol instability test +ve

Acquired haemolytic anaemias ^[1]^[15]:

Category	Examples	Key Distinguishing Features
Immune	Warm AIHA (IgG), Cold AIHA (IgM)	DAT (direct antiglobulin test) positive ^[14]; spherocytes (warm) or agglutination (cold)
Mechanical / fragmentation	MAHA (TTP, HUS, DIC), prosthetic valve	Schistocytes on smear; thrombocytopenia in TTP/HUS
Infection	Malaria	Travel history (TOCC); ring forms on thick/thin smear
Membrane defect (acquired)	PNH	Flow cytometry for GPI-anchored proteins (CD55, CD59); haemoglobinuria; thrombosis
Hypersplenism	Liver disease, portal hypertension	Pancytopenia + splenomegaly; underlying liver disease
Drug-induced	Oxidant drugs, immune-mediated	Drug history; temporal correlation

3. Differential Diagnosis Within Thalassemia Syndromes

Once you've established "this is thalassemia," the next question is: which type and how severe?

Feature	α-Thalassemia	β-Thalassemia
Age of onset	In utero (severe) or neonatal	3–6 months (major); older (intermedia/trait)
HbA₂	Normal or ↓	↑ in β-thal trait (> 3.5%)
HbF	Normal (trait/HbH); ↑ with Hb Bart's at birth	↑ in β-thal major/intermedia
HbH (β₄) on Hb study	Present (α-thal intermedia / HbH disease)	Absent
Hb Bart's (γ₄)	Present in newborn screen (severe α-thal)	Absent
HbH inclusions (supravital stain)	Present	Absent
Molecular basis	Deletions (usually) — SEA deletion common in HK	Point mutations (usually)
Diagnosis confirmatory	DNA / molecular analysis	Hb study (HPLC/CE) + DNA if needed

Excess beta chain binds with themselves, creating a β₄ tetramer → Haemoglobin H. This is useless, unstable, with a high oxygen affinity → cannot deliver oxygen. So this helps with diagnosis → excess beta chain infers that there is not enough alpha chains ^[2]. This is the basis of the indirect diagnostic approach — since direct quantification of globin chain production is impractical, we detect the excess unpaired chains to infer the deficit.

Haemoglobinopathies do NOT typically affect MCV — most patients with structural Hb variants (HbS, HbC) have a normal MCV ^[2]. So if you see microcytosis, think thalassemia first. The triggers for investigating haemoglobinopathy are different ^[2]:

Clinical Feature	Corresponding Laboratory Finding
Pallor, jaundice, splenomegaly	Haemolysis → as seen in some unstable Hb
Plethora	Erythrocytosis → as seen in some Hb with high oxygen affinity
Cyanosis	Methemoglobin, low SaO₂ → as seen in patients with HbM

"Not MCV — most haemoglobinopathies do not affect MCV" ^[2].

The exception: thalassemic haemoglobinopathies (e.g. HbE, Hb Constant Spring) where the abnormal Hb is also produced at a reduced rate, so MCV is low ^[1].

The Diagnostic Trap of α-Thalassemia Trait

α-thalassemia trait (1 or 2 gene deletion) is the most difficult thalassemia to diagnose because:

HbA₂ is normal (not elevated like β-thal trait)
No HbH is present (unlike HbH disease)
MCV may be normal with single gene deletion
The only reliable method is DNA / molecular analysis (e.g. PCR for SEA deletion, multiplex ligation-dependent probe amplification [MLPA])
In practice, α-thal trait is often a diagnosis of exclusion: microcytic anaemia + normal iron studies + normal HbA₂ + negative for other causes → suspect α-thal trait → confirm with DNA

5. Key Differentials in Specific Clinical Scenarios

Differential	Distinguishing Feature
Hb Bart's hydrops fetalis (α-thal major)	Hb electrophoresis: > 80% Hb Bart's (γ₄); both parents α-thal trait (cis type)
Immune hydrops (Rh/ABO HDN)	Positive DAT on cord blood; maternal antibodies
Non-immune hydrops (cardiac, infectious, chromosomal)	Echocardiography, TORCH screen, karyotype
Congenital infection (parvovirus B19, CMV)	Serology, PCR

Differential	Distinguishing Feature
β-thalassemia major	Hb study: ↑ HbF (60–90%), ↓ or absent HbA; parents both β-thal trait
Severe iron deficiency (dietary)	Iron studies abnormal; responds to iron supplementation
Congenital dyserythropoietic anaemia (CDA)	Rare; morphological features on BM; specific gene mutations
Diamond–Blackfan anaemia (DBA)	Pure red cell aplasia; ↓ reticulocytes; macrocytic; associated congenital anomalies

Think: thalassemia trait vs IDA vs ACD — use the table and algorithm above.

Thalassemia causes variable effects on HbA1c ^[7]:

In haemolytic states → shortened RBC lifespan → falsely low HbA1c
This means HbA1c is unreliable for diabetes monitoring in thalassemia patients
Alternatives: fructosamine, glycated albumin, continuous glucose monitoring

Thalassemia patients are prone to delayed haemolytic transfusion reactions ^[8] — because chronically transfused patients develop antibodies to minor blood group antigens (e.g. Kidd). Initial antibody titre may be too low to detect on type-and-screen, but re-exposure triggers an anamnestic response → haemolysis at 4–5 days post-transfusion.

"Especially in thalassemia patients" — who receive the most transfusions and are therefore at highest risk of alloimmunisation ^[8].

For transfusion, thalassemia patients should receive the newest bag of blood (freshest red cells, for optimal post-transfusion survival and oxygen delivery), whereas immunocompromised patients needing irradiated products in an emergency should receive the oldest bag (lymphocytes dead after > 14 days of storage) ^[8].

High Yield Summary — Differential Diagnosis of Thalassemia

Microcytic anaemia DDx (TAILS): Thalassemia, ACD, IDA, Lead poisoning, Sideroblastic anaemia. In HK, the two most common causes are IDA and thalassemia ^[9].
Thal trait vs IDA: Use RBC count (↑ in thal, ↓ in IDA), RDW (normal in thal, ↑ in IDA), iron studies (normal in thal, abnormal in IDA), HbA₂ (↑ in β-thal trait), blood smear (target cells + basophilic stippling in thal vs pencil cells in IDA) ^[2]^[9]^[13].
α-thal vs β-thal: HbA₂ ↑ in β-thal trait; HbH present in α-thal intermedia; DNA analysis needed for α-thal trait diagnosis.
Thalassemia vs haemoglobinopathy: Thalassemia = low MCV (quantitative); haemoglobinopathy = usually normal MCV (qualitative). "Not MCV — most haemoglobinopathies do not affect MCV" ^[2].
Reticulocyte count is inappropriately low in thalassemia major (ineffective erythropoiesis) — unlike other haemolytic anaemias where reticulocytes are high ^[3]^[4].
Always consider co-existing pathology when anaemia severity exceeds what thalassemia alone can explain ^[2].

Active Recall - Thalassemia Differential Diagnosis

References

^[1] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (Disorders of hemoglobin section; Inherited haemolytic anaemia classification) ^[2] Senior notes: Block A - Many members of the family have anaemia.pdf (Thal trait vs IDA differentiation; Haemoglobinopathy triggers; Diagnostic approach) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Diagnosis section — reticulocyte count, physical examination, biochemical tests) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Diagnosis section — reticulocyte count, physical examination, biochemical tests) ^[7] Senior notes: Block A - Polyuria and polydipsia_ glucose metabolism; diabetes mellitus; diabetic ketoacidosis.pdf (HbA1c limitations in thalassemia) ^[8] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (Delayed haemolytic transfusion reactions; newest vs oldest bag; haemosiderosis) ^[9] Senior notes: Block A - Introduction to Haematological investigations (CBP, Clotting).pdf (Two most common causes of microcytic anaemia in HK; PBS comparison; Sin vs Hwang methods) ^[10] Lecture slides: GC 097. Many members of the family have anaemia (File 2).pdf (Triggers for lab diagnosis of thalassemia) ^[11] Lecture slides: GC 097. Many members of the family have anaemia (PATH).pdf (Triggers for lab diagnosis of thalassemia) ^[12] Senior notes: Block A - Pallor_ diagnosis of anaemia; nutritional anaemia; anaemia of systemic diseases.pdf (MCV-based classification; sideroblastic anaemia; intramedullary haemolysis DDx) ^[13] Senior notes: Block A - Many members of the family have anaemia.pdf (Blood smear comparison; RDW vs RBC count methods; target cells vs pencil cells) ^[14] Lecture slides: Haematology Introduction to Haematological investigations (CBP, Clotting).pdf (Haemolytic anaemia laboratory features) ^[15] Senior notes: Maksim Medicine Notes.pdf (Haemolytic anaemia classification and workup)

Diagnostic Criteria, Algorithm and Investigations for Thalassemia

Unlike many conditions (e.g. SLE with ACR criteria, or DM with glucose thresholds), thalassemia does not have a single set of universally published "diagnostic criteria" with a numerical score. Instead, diagnosis is built by layering evidence from clinical suspicion → CBC → haemoglobin study → molecular/DNA analysis. Think of it as a stepwise process where each tier narrows the diagnosis further.

The practical "diagnostic criteria" are:

Clinical or CBC trigger — low MCV +/- clinical features (pallor, splenomegaly, failure to thrive, family history) ^[2]^[10]^[11]
Haemoglobin study (HPLC / capillary electrophoresis) — quantifies HbA, HbA₂, HbF, and detects abnormal haemoglobins (HbH, Hb Bart's, HbE, etc.)
Molecular / DNA analysis — identifies the specific mutation or deletion (essential for α-thalassemia confirmation and prenatal diagnosis)

GC High Yield — Triggers for Laboratory Diagnosis of Thalassemia

Triggers for laboratory diagnosis of thalassemia: Low MCV +/- Clinical features (pallor, splenomegaly, failure to thrive) ^[10]^[11]. MCV is now found in all CBC reports ^[2] — meaning every single CBC you order is already screening for thalassemia.

The diagnostic process is best understood as a flow. We start with the CBC (which every patient gets), then proceed through iron studies, haemoglobin study, and finally DNA analysis depending on what we find.

The approach to laboratory diagnosis of thalassemia is summarised in this workflow ^[2]. The key concept: the diagnosis of thalassemia is indirect — since direct quantification of globin chain production is impractical, we detect excess unpaired chains (e.g. HbH = β₄, Hb Bart's = γ₄) or shifts in HbA₂/HbF ratios to infer the globin chain deficit ^[2].

The Indirect Diagnostic Logic

Why is the diagnosis "indirect"? Because you'd think that for a quantitative defect, you'd simply measure how much α-chain vs β-chain the patient is producing. But the steps to directly quantify globin chain production are cumbersome, and no labs apart from research labs would do such a thing for diagnosis ^[2]. Instead, we detect the consequences of imbalanced production — the excess unpaired chains forming abnormal tetramers (HbH, Hb Bart's) or the compensatory shifts (↑ HbA₂, ↑ HbF) — and reason backwards to the deficit.

3. Investigation Modalities — Detailed Interpretation

This is the first-line investigation and often the initial clue.

Parameter	Expected Finding in Thalassemia	Interpretation / Why
Haemoglobin	Trait: 10–13 g/dL; Intermedia: 6–10 g/dL (β) / 7–11 g/dL (α); Major: < 6 g/dL ^[3]^[4]	Reflects severity of globin chain deficit → more chains missing → worse anaemia
MCV	Low (< 80 fL) — in trait, usually not < 65 fL ^[2]	Reduced Hb per cell → cells undergo extra divisions → smaller cells. The microcytosis in thal is uniform (all cells equally affected by the genetic defect)
MCH	Low	Less haemoglobin in each cell → hypochromia
RBC count	Normal or increased ^[2]^[6]^[9]	The bone marrow is functionally normal (in trait) — it compensates by making MORE cells (each carrying less Hb). This is a key differentiator from IDA, where the marrow lacks raw material and makes FEWER cells
RDW	Normal or slightly high ^[2]^[9]^[13]	Genetic defect → all RBCs equally affected → uniform microcytosis → low variation in size. In IDA, iron levels fluctuate → cells produced at different iron availabilities → high RDW
Reticulocyte count	Inappropriately low for degree of anaemia (commonly < 8%) in major ^[3]^[4]; modestly elevated in intermedia/HbH	In thal major: ineffective erythropoiesis dominates — precursors die in marrow before becoming reticulocytes. In HbH disease: some reticulocytosis because peripheral haemolysis triggers compensatory marrow response
Platelet count	Usually normal; can be elevated post-splenectomy
WBC count	Usually normal

GC High Yield — CBC Approach to Microcytic Anaemia

In HK, the two most common causes of hypochromic microcytic anaemia: (1) Iron deficiency anaemia, (2) Thalassemia ^[9].

Two methods to distinguish:

Sin: RDW → higher = IDA (acquired, varying iron levels → unequal cell sizes); lower = thalassemia (genetic, all cells equally affected) ^[9]
Hwang: RBC count → > 5×10¹²/L often thalassemia; < 5×10¹²/L often IDA. Formally use the Mentzer index (MCV ÷ RBC count): < 13 = thalassemia, > 13 = IDA ^[6]^[9]

The PBS provides morphological clues and is often described as "blood smear is king" ^[13].

Finding	Seen In	Pathophysiological Basis
Hypochromia (low MCH) + Microcytosis (low MCV) ^[9]	Both thalassemia and IDA	Reduced Hb content per cell
Target cells	Thalassemia (also in IDA, liver disease, HbC)	Relative excess of membrane compared to cell volume → membrane folds centrally when dried on slide
Basophilic stippling	Thalassemia — "the major feature distinguishing the two" ^[9]	Precipitated ribosomal RNA aggregates in the cytoplasm. In thalassemia, the excess unpaired globin chains aggregate with ribosomal material. This is NOT typically seen in IDA
Anisocytosis and Poikilocytosis ^[3]^[4]^[9]	Thalassemia (moderate-severe)	Varied cell sizes (aniso-) and shapes (poikilo-) from damaged and abnormal red cells
Teardrop cells (dacrocytes) ^[3]^[4]	Thalassemia (moderate-severe)	Cells damaged by splenic pitting of inclusions → distorted shape
Nucleated RBCs (NRBCs)	Thalassemia major, post-splenectomy	Massively expanded and ineffective erythropoiesis → premature release of immature precursors
Pencil cells / Elliptocytes	IDA ^[9]	Characteristic of iron-deficient erythropoiesis — NOT typical of thalassemia
Polychromasia	More in haemolytic phase / HbH disease	Reticulocytes staining bluish-purple due to residual RNA
Uniform vs Non-uniform cell size	Thalassemia = uniform; IDA = non-uniform ^[13]	Genetic (constant) vs acquired (fluctuating) defect

Peripheral blood smear for thalassemia: RBCs are hypochromic (low MCH) and microcytic (low MCV); Anisocytosis and Poikilocytosis; Target cells, spherocytes, schistocytes; Basophilic stippling ^[9].

Peripheral blood smear for IDA: RBCs are hypochromic + microcytic; Variations in size and shape (High RDW); Pencil cells / elliptocytes, Target cells; No polychromasia; Reactive thrombocytosis ^[9].

Iron studies serve two purposes: (a) exclude IDA as the cause of microcytosis, (b) detect iron overload in established thalassemia.

Parameter	Thalassemia Trait	Iron Deficiency	Thalassemia with Iron Overload
Serum iron	Normal	Decreased	↑
TIBC	Normal	Increased	Normal or ↓
Transferrin saturation (TSAT)	Normal	Decreased	> 45%
Serum ferritin	Normal	Decreased	↑↑ (> 1000 μg/L suggests significant overload)

Why is TIBC high in IDA? Because the body is desperately trying to scavenge every bit of iron available → it upregulates transferrin production → more iron-binding capacity. In thalassemia trait, there's no iron deficit, so TIBC stays normal ^[2]^[6]^[15].

Rationale for measuring ferritin in thalassemia intermedia ^[2]: There is a risk of iron overload from increased gut iron absorption (driven by ineffective erythropoiesis suppressing hepcidin) plus any transfusions. Ferritin is a surrogate marker for iron stores. With iron overload, haemosiderin concentration increases in macrophages → iron leaks into cytoplasm, damaging macrophages → ferritin leaks out → serum ferritin rises ^[2].

Iron Overload Monitoring — MRI T2*

For established thalassemia patients on regular transfusions, serum ferritin alone is insufficient for monitoring iron overload because it is an acute phase reactant (confounded by infection, inflammation, liver disease). MRI T2 of the liver and heart* is the gold standard — it directly measures tissue iron concentration non-invasively ^[8].

Liver MRI T2*: < 6.3 ms = severe iron overload; 6.3–11.4 ms = moderate; > 11.4 ms = mild/normal
Cardiac MRI T2*: < 10 ms = severe cardiac iron (high risk of heart failure/arrhythmia); 10–20 ms = moderate; > 20 ms = normal

Iron in 500 mL of blood = 250 mg. Only 1 mg of iron excreted per day. The body does not have a good mechanism of iron excretion ^[6]^[8].

This is the key investigation that separates thalassemia subtypes from each other and from other haemoglobinopathies. Methods include:

HPLC (High-Performance Liquid Chromatography) — most commonly used in HK; separates Hb variants by charge
Capillary electrophoresis (CE) — alternative method with similar performance
Hb electrophoresis — traditional method, still used in some settings

Memory anchor: normal haemoglobins pair 2 α chains with 2 non-α chains: HbA = α₂β₂, HbA₂ = α₂δ₂, HbF = α₂γ₂. If α chains are missing, the leftovers make “four of a kind”: adult β₄ = HbH; fetal γ₄ = Hb Bart's.

β-thal patternα-thal patternNormal / equivocalStructural variant

Haemoglobin study findings, globin-chain composition, diagnoses, and explanations
Hb study finding	Hb name & globin chains	Diagnosis	Explanation
β-thal pattern HbA₂ ≥ 3.5% (typically 4–8%)	HbA₂ minor adult haemoglobin Chains: α₂δ₂ (2 α + 2 δ)	*β-thalassaemia trait*	With reduced β-chain production, δ-chain pairing becomes relatively more prominent, so HbA₂ rises. This is the single most important Hb study finding for β-thalassaemia trait.
β-thal pattern HbA₂ ≥ 3.5% + ↑↑ HbF (10–90%)	HbA₂ minor adult haemoglobin Chains: α₂δ₂ (2 α + 2 δ) HbF fetal haemoglobin Chains: α₂γ₂ (2 α + 2 γ)	*β-thalassaemia major or intermedia*	With severely reduced or absent β-chain production, γ-chain production persists or is reactivated as compensation, so HbF rises dramatically.
α-thal pattern *HbH band (fast-migrating) detected*	HbH β-chain tetramer Chains: β₄ (4 β; no α)	*HbH disease (α-thalassaemia intermedia)*	When α chains are deficient after birth, the excess β chains form the unstable β₄ tetramer HbH, which produces a fast-migrating band.
α-thal pattern *Hb Bart's detected (newborn screen)*	Hb Bart’s fetal γ-chain tetramer Chains: γ₄ (4 γ; no α; “Bart’s” is an eponym)	*α-thalassaemia (severity depends on proportion)*	When α chains are deficient before birth, excess γ chains form Hb Bart's. Small amounts (1–2%) suggest α-thalassaemia trait; large amounts suggest HbH disease or Hb Bart's hydrops fetalis.
Normal / equivocal *Normal HbA₂, normal HbF, no HbH*	HbA₂ minor adult haemoglobin (normal here) Chains: α₂δ₂ HbF fetal haemoglobin (normal here) Chains: α₂γ₂ HbH β-chain tetramer (absent here) Chains: β₄	*α-thalassaemia trait (1–2 gene deletion) or normal*	Mild α-thalassaemia may create too little chain imbalance to generate detectable HbH or alter HbA₂. Diagnosis requires DNA analysis.
Structural variant *Abnormal Hb band at a specific retention time*	HbE / HbS / HbC named β-globin variants Chains: α₂βᴱ₂ / α₂βˢ₂ / α₂βᶜ₂ (the β chain is structurally altered) Hb Constant Spring elongated, unstable α-globin variant Chains: αᶜˢ (the variant is an α chain)	*Haemoglobinopathy (HbE, HbS, HbC, HbCS, etc.)*	Each structural Hb variant has a characteristic elution time or migration pattern. Its letter or place-name identifies a variant, not a separate normal globin-chain class.

Why HbA₂ Rises in β-Thal Trait — From First Principles

Normal adults: α₂β₂ = HbA (~97%), α₂δ₂ = HbA₂ (~2.5%). The β and δ genes are both on chromosome 11 and "compete" for α-chains. When β-chain production falls (β-thal trait), more α-chains become available to pair with δ-chains → HbA₂ (α₂δ₂) increases proportionally. This is why HbA₂ ≥ 3.5% is diagnostic of β-thal trait ^[2]^[3]^[4].

Pitfall: If the patient also has concurrent iron deficiency, δ-chain production is suppressed → HbA₂ may be falsely normalised → you might miss β-thal trait. Always correct iron deficiency first, then recheck HbA₂.

Supravital staining with brilliant cresyl blue (BCB) or new methylene blue is a simple, quick test specifically for α-thalassemia:

In HbH disease: Multiple HbH inclusion bodies appear as "golf ball"-like inclusions scattered throughout red cells — these represent precipitated β₄ tetramers
Heinz bodies represent clumped inclusion bodies of precipitates of α-globin within RBCs, more readily appreciated by staining with methyl violet or other supravital stains ^[3]^[4]
In β-thal major (post-splenectomy): α-chain inclusions (Heinz bodies) are visible — these represent precipitated excess α-chains

This is a bedside/laboratory test that can rapidly suggest α-thal when HbH inclusions are found.

Hb pattern: HbH inclusion bodies — listed as a key laboratory finding for α-thalassemia ^[15].

This is the definitive diagnostic test and is essential in several situations:

Indication	Reason
Confirming α-thal trait	Hb study is normal in 1–2 gene deletions; DNA is the only way to confirm
Prenatal diagnosis	Must identify the specific mutation/deletion in both parents to predict offspring genotype
Distinguishing β⁰ from β⁺	Determines if patient is making zero or reduced β-chain → predicts clinical severity
Detecting non-deletional variants	e.g. Hb Constant Spring (stop codon mutation) requires sequencing
Pre-implantation genetic diagnosis	For couples undergoing IVF to avoid affected embryos

Methods:

Gap-PCR: Detects common deletions (e.g. SEA deletion, 3.7 deletion, 4.2 deletion)
MLPA (Multiplex Ligation-dependent Probe Amplification): Detects less common/novel deletions
DNA sequencing: Identifies point mutations (essential for β-thal genotyping)
ARMS-PCR (Amplification Refractory Mutation System): Targets known point mutations

Alpha-IC strip for Hb Barts; Alpha genotyping ^[15] — rapid immunochromatographic strip tests can detect Hb Bart's in newborn blood, and genotyping confirms the specific deletion.

In more severe thalassemia (intermedia, major, HbH disease), markers of haemolysis should be checked:

Parameter	Expected Finding	Why
↑ Unconjugated bilirubin ^[3]^[4]^[1]	Pre-hepatic jaundice from RBC destruction	Haem from destroyed RBCs is converted to unconjugated bilirubin → overwhelms liver conjugation capacity
↑ LDH ^[3]^[4]^[1]	Released from destroyed RBCs	LDH is abundant in RBC cytoplasm; its elevation is the quickest way to differentiate haemolysis from non-haemolytic anaemia ^[1]
↓ Haptoglobin ^[3]^[4]^[1]	Consumed by binding free Hb	Haptoglobin scavenges free haemoglobin released from lysed RBCs → gets used up. Note: Haptoglobin deficiency is common in Chinese (1:1000) ^[8] — may be baseline low
↑ AST ^[3]^[4]	Released from destroyed RBCs	AST is also present in RBCs (unlike ALT, which is more liver-specific)
↑ Serum uric acid ^[3]^[4]	Increased nucleic acid turnover	Massively expanded but ineffective erythropoiesis → high purine catabolism
↑ Methaemalbumen ^[1]	Haptoglobin saturated → free haem binds albumin	Once haptoglobin is fully consumed, haem binds to albumin → methaemalbumen

Investigation	Purpose	Key Findings
Skull X-ray	Assess marrow expansion	"Hair-on-end" / "crew-cut" appearance — widened diploic space with perpendicular trabeculae radiating outward from inner table; thinning of cortex ^[15]
Abdominal USS	Assess spleen and liver size; gallstones	Hepatosplenomegaly, pigment gallstones
MRI T2 liver and heart*	Iron overload monitoring ^[8]	T2* shortening proportional to iron content. Cardiac T2* < 20 ms = iron loading; < 10 ms = severe
Echocardiography	Cardiac function	LV dysfunction, pulmonary hypertension (especially in NTDT)
Endocrine panel	Iron overload damage to endocrine organs	TFTs (hypothyroidism), glucose/HbA1c (diabetes — but HbA1c unreliable in thalassemia ^[7]), LH/FSH/testosterone or oestradiol (hypogonadism), calcium/PTH (hypoparathyroidism), IGF-1/GH (growth failure)
DEXA scan	Osteoporosis assessment	Reduced BMD from marrow expansion + iron overload + endocrinopathy
Liver function tests	Hepatic iron overload, viral hepatitis (from transfusions)	Deranged ALT/AST; check HBV/HCV serology

Test	Timing	Purpose
Parental Hb study + iron studies	Pre-conception or early pregnancy	Identify at-risk couples (both carriers)
CVS + DNA analysis	10–12 weeks gestation	Early prenatal diagnosis — identify foetal genotype
Amniocentesis + DNA analysis	16–19+6 weeks gestation	Alternative to CVS; slightly later
Cordocentesis + Hb study	≥ 18 weeks	If USS abnormal — confirms diagnosis on foetal blood
Serial USS	13, 16, 20, 30 weeks	Detect features of Hb Bart's hydrops: cardiomegaly, placentomegaly, IUGR, hydropic changes ^[4]
Newborn screening (cord blood Hb study)	At delivery	Detects Hb Bart's, HbH, HbF proportions — used in universal or targeted newborn screening programmes

Type	CBC	Hb Study	Haemolysis Markers	DNA Analysis
α-thal silent carrier (1 gene)	Normal or borderline ↓ MCV	Normal	Normal	Confirms deletion
α-thal trait (2 genes)	↓ MCV, ↑ RBC, mild/no anaemia	Normal HbA₂, no HbH	Normal	Essential — only way to diagnose
HbH disease (3 genes)	↓ MCV, moderate anaemia (7–11 g/dL)	HbH present (5–30%), ↓ HbA₂	↑ Unconj. bili, ↑ LDH, ↓ haptoglobin	Confirms deletion type
Hb Bart's (4 genes)	Severe anaemia, NRBCs	> 80% Hb Bart's (γ₄)	Massive haemolysis	Confirms --/--
β-thal trait (β/β⁰ or β/β⁺)	↓ MCV, ↑ RBC, mild/no anaemia	HbA₂ ≥ 3.5%	Normal	Optional (for genotyping)
β-thal intermedia	↓ MCV, Hb 6–10 g/dL	↑ HbA₂, ↑↑ HbF	Mild–moderate haemolysis	Identifies specific mutations
β-thal major	↓↓ MCV, Hb < 6 g/dL	↑ HbA₂, ↑↑↑ HbF (60–90%), ↓↓ or absent HbA	Significant haemolysis + ineffective erythropoiesis	Identifies β⁰ vs β⁺; for family counselling

High Yield Summary — Diagnosis of Thalassemia

Triggers: Low MCV +/- clinical features (pallor, splenomegaly, failure to thrive) ^[10]^[11].
Step 1 — CBC: Low MCV + high RBC count suggests thalassemia over IDA. Mentzer index < 13 → thalassemia; > 13 → IDA ^[6]^[9].
Step 2 — Iron studies: Normal iron studies excludes IDA and points towards thalassemia. Abnormal iron studies may indicate coexisting IDA (correct first, then reassess).
Step 3 — Hb study (HPLC/CE): HbA₂ ≥ 3.5% = β-thal trait. HbH detected = α-thal intermedia (HbH disease). Normal Hb study with persistent microcytosis → suspect α-thal trait → DNA analysis.
Step 4 — DNA analysis: Essential for α-thal trait confirmation, prenatal diagnosis, and genotyping for genetic counselling.
PBS features of thalassemia: hypochromia, microcytosis, target cells, basophilic stippling (distinguishing feature from IDA), teardrop cells, NRBCs.
Haemolysis screen: ↑ LDH, ↑ unconjugated bilirubin, ↓ haptoglobin, ↑ AST.
Iron overload monitoring: MRI T2 of liver and heart* (gold standard); serum ferritin (screening/trending).
Reticulocyte count is inappropriately low in β-thal major (ineffective erythropoiesis) despite severe anaemia.
Prenatal: CVS at 10–12 weeks or amniocentesis at 16–19 weeks with DNA analysis; serial USS for hydrops features.

Active Recall - Thalassemia Diagnosis and Investigations

References

^[1] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (Haemolytic anaemia laboratory features; LDH as key differentiator) ^[2] Senior notes: Block A - Many members of the family have anaemia.pdf (Diagnostic workflow; thal trait vs IDA differentiation table; ferritin rationale; indirect diagnostic logic; HbH explanation) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Diagnosis section — CBC, PBS, supravital staining, haemolysis markers) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Diagnosis section — CBC, PBS, supravital staining, haemolysis markers; prenatal diagnostic strategy) ^[6] Senior notes: Block A - Hematology Interactive Tutorial.pdf (Mentzer index; RBC count differentiation; iron in blood; chelation) ^[7] Senior notes: Block A - Polyuria and polydipsia_ glucose metabolism; diabetes mellitus; diabetic ketoacidosis.pdf (HbA1c unreliability in thalassemia) ^[8] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (MRI T2*; iron chelation; haptoglobin deficiency in Chinese; haemosiderosis; oldest vs newest bag) ^[9] Senior notes: Block A - Introduction to Haematological investigations (CBP, Clotting).pdf (Two most common causes in HK; PBS comparison; RDW vs RBC count methods; basophilic stippling) ^[10] Lecture slides: GC 097. Many members of the family have anaemia (File 2).pdf (Triggers for lab diagnosis) ^[11] Lecture slides: GC 097. Many members of the family have anaemia (PATH).pdf (Triggers for lab diagnosis) ^[13] Senior notes: Block A - Many members of the family have anaemia.pdf (Blood smear comparison; uniform vs non-uniform) ^[15] Senior notes: Maksim Medicine Notes.pdf (Thalassemia laboratory findings summary; alpha-IC strip; Hb pattern)

Management of Thalassemia

The management of thalassemia is best understood by thinking about what we're actually trying to fix at each level of disease severity. Everything flows from the pathophysiology:

Pathological Process	Management Strategy
Insufficient functional Hb → anaemia	Transfusion (supply exogenous normal RBCs)
Ineffective erythropoiesis → marrow expansion, iron absorption	Transfusion (suppresses endogenous erythropoiesis), iron chelation (removes excess iron)
Haemolysis → splenomegaly → increased transfusion requirements	Splenectomy (removes site of RBC destruction)
Underlying genetic defect	Allogeneic HSCT (replace defective marrow), gene therapy (correct the gene)
Iron overload → organ damage	Iron chelation, dietary iron restriction, monitoring

The intensity of management is determined by where the patient falls on the severity spectrum:

This is the mildest form — patients are generally asymptomatic and require no treatment for anaemia.

Reassurance: Explain to the patient that they have a genetic carrier state, NOT a disease requiring treatment
Avoid misdiagnosis as IDA: Do NOT prescribe iron supplements unless concurrent IDA is documented ^[2]^[16]. Inappropriate iron in a thalassemia trait patient can cause iron overload over time
Genetic counselling: Detection of carrier state in order to provide genetic counselling ^[2]. If both partners are carriers → 25% risk of severely affected offspring. "For the patient, for the carrier, for the unborn" ^[2]
Low iron diet is generally unnecessary for trait (only relevant for intermedia/major)

Common Exam Mistake — Iron for Thalassemia Trait

A very common error is prescribing iron to a patient with thalassemia trait after seeing a low MCV. The MCV will NOT improve with iron because the microcytosis is genetic, not nutritional. Always check iron studies first. Iron supplements are contraindicated in thalassemia unless there is documented concurrent iron deficiency.

3. Management of Thalassemia Intermedia (NTDT)

These patients (HbH disease, β-thal intermedia) have moderate anaemia (Hb 6–10 g/dL) and do not require lifelong transfusion ^[2], but they need ongoing surveillance and intermittent interventions.

Folate supplementation for all thal major and thal intermedia with chronic haemolysis ^[16]^[17]
- Dose: 1–2 mg/day ^[16]^[17]
- Why? Chronic haemolysis → increased RBC turnover → increased folate consumption for DNA synthesis in the expanded erythroid marrow. Without supplementation, folate deficiency develops, worsening the anaemia (megaloblastic change on top of microcytic baseline)
Low iron diet (e.g. avoid excess red meat, spinach) ^[16]^[17]
- Why? Ineffective erythropoiesis suppresses hepcidin → increased gut iron absorption → iron overload even WITHOUT transfusions. Restricting dietary iron intake mitigates this

Indication: SELECTED thal intermedia ^[16]^[17], including:

As needed, during erythropoietic stress (e.g. infection, surgery, pregnancy) ^[16]^[17]
Anaemic complications (e.g. cardiopulmonary compromise, decreased functioning, decreased QoL, growth failure, poor feeding) ^[17]
Significant extramedullary haematopoiesis (e.g. bony masses, hypersplenism, pathological fractures) ^[17]

Ferritin is a surrogate marker for iron stores ^[2] — check regularly even in non-transfused patients
MRI T2 liver* annually if ferritin elevated
Start chelation if evidence of significant iron overload (see section 4.3)

4. Management of Thalassemia Major (TDT)

This is the full management programme for transfusion-dependent patients. It has four pillars: (A) Regular transfusion, (B) Iron chelation, (C) Splenectomy (when indicated), (D) Curative therapy (HSCT / gene therapy).

4.1 Regular Blood Transfusion — The Mainstay

Regular transfusion is the mainstay of treatment ^[16]^[17] for all thalassemia major and selected severe intermedia patients.

Goals of transfusion: ^[3]^[4]

Pre-transfusion Hb = 9.5–10.5 g/dL
Post-transfusion Hb = 14 g/dL (to suppress bone marrow hyperactivity)
Avoid post-transfusion Hb > 15 g/dL due to increased risk of viscosity and thrombosis ^[3]^[4]

Why these targets? The logic is beautiful:

Keeping pre-transfusion Hb above ~9.5 g/dL ensures adequate oxygen delivery, prevents symptoms, and — critically — suppresses the patient's own ineffective erythropoiesis. When you provide enough exogenous normal RBCs, the erythropoietin drive drops, the bone marrow calms down, and the downstream consequences (marrow expansion → skeletal deformities, extramedullary haematopoiesis, iron hyperabsorption) are all minimised
But don't overshoot > 15 g/dL → hyperviscosity, thromboembolism risk increases

Transfusion should be given at an interval of 4 weeks ^[3]^[4] — this is the "hypertransfusion" regimen. Some patients may need transfusions every 2–3 weeks depending on their rate of Hb decline.

Use of blood products ^[3]^[4]:

Requires pre-filtered products that are leukocyte depleted — reduces febrile non-haemolytic transfusion reactions (from recipient antibodies against donor WBC antigens) and CMV transmission
Matched for at least D, C, c, E, e and Kell antigens — this is extended antigen matching beyond standard ABO/Rh(D), to minimise alloimmunisation in chronically transfused patients. Why? Because thalassemia patients receive dozens to hundreds of transfusions over their lifetime → cumulative exposure to minor blood group antigens → high risk of developing alloantibodies → future cross-match difficulties and delayed haemolytic transfusion reactions ^[8]
CMV-negative blood products are indicated in HSCT candidates ^[3]^[4] — because CMV reactivation post-transplant in an immunosuppressed patient can be fatal

For thalassemia patients, ask the blood bank for the newest bag of blood ^[8]. Fresh RBCs have the longest post-transfusion survival and best oxygen-carrying capacity, maximising the interval between transfusions.

Pre-medications ^[3]^[4]:

IV/PO Chlorpheniramine (Piriton) 30 minutes before transfusion — antihistamine to prevent allergic/urticarial reactions
IV Furosemide (Lasix) at the start of transfusion — to prevent fluid overload (these patients receive regular large-volume transfusions and may have cardiac dysfunction from iron overload)
NO folate supplement required once on regular transfusion ^[3]^[4] — why? Because the regular transfusion programme suppresses the patient's own erythropoiesis (that's the whole point), so folate consumption drops. The transfused RBCs are already fully formed and don't require folate

Folate Supplementation Logic

Not on regular transfusions (intermedia, pre-transfusion era): Folate 1–2 mg/day ^[16]^[17] — active endogenous erythropoiesis consumes folate
On regular transfusions (thal major on hypertransfusion): NO folate needed ^[3]^[4] — endogenous erythropoiesis is suppressed

Monitor for ^[3]^[4]:

Acute haemolytic transfusion reaction (ABO incompatibility — most dangerous)
Febrile non-haemolytic transfusion reaction (FNHTR)
Allergic (urticarial) transfusion reaction
Bacterial contamination reaction

Monitoring ^[17]:

Pre-transfusion: Hb, cross-match, ferritin, urine glucose
Post-transfusion: Hb
Every 6 months: serum Ca/PO₄, blood glucose/fructosamine/HbA1c, TFTs, infection screen (HIV, HBV, HCV)
Every year: endocrine assessment, cardiac assessment (MUGA scan, ECG, CXR, cardiac MRI T2*), serum zinc, ophthalmology and audiology review (chelation toxicity), DEXA scan

HbA1c is unreliable in thalassemia ^[7] — use fructosamine or glycated albumin for diabetes monitoring. Serum Ca/PO₄, TFTs, LH/FSH/testosterone screen for iron overload endocrinopathies.

4.3 Iron Chelation Therapy

Iron overload is the leading cause of death in transfusion-dependent thalassemia. Each unit of packed RBCs delivers ~200–250 mg of iron, and the body does not have a good mechanism of iron excretion ^[6]. Without chelation, iron accumulates in the heart (→ cardiomyopathy), liver (→ fibrosis/cirrhosis), and endocrine organs (→ diabetes, hypogonadism).

Indications of iron chelation ^[3]^[4]^[17]:

Patient ≥ 3 years old
Serum ferritin > 2000 ng/mL
Transfusion > 20 units

(In practice, current TIF 2024 guidelines recommend starting chelation earlier, after ~10–20 transfusions or when ferritin exceeds 1000 ng/mL, but the above are the thresholds taught in HKUMed lectures.)

Aim: target serum ferritin 1000–2000 ng/mL ^[3]^[4]^[17], liver iron concentration (LIC) 3–7 mg/g dry weight, and cardiac MRI T2 > 20 ms (monitored annually from ≥ 8 years old)* ^[17].

Three types: 1 is subcutaneous/IV, 2 are oral ^[6]^[8]:

Chelator	Route	Dosing	Mechanism	Side Effects	Key Points
Deferoxamine (DFO / Desferal)	SC / IV	20–50 mg/kg/day SC, 5–6 days/week ^[3]^[4]^[17]	Hexadentate chelator — binds Fe³⁺ in a 1:1 ratio → excreted via urine (reddish) and faeces	Ototoxicity, retinal damage, bone dysplasia with truncal shortening ^[3]^[4]	MOST studied iron chelator with excellent safety and efficacy profile ^[3]^[4]. Half-life < 30 min, requiring prolonged infusion (8–12 hours). Major compliance issue due to inconvenience of SC pump
Deferiprone (DFP / L1)	Oral (TDS)	75–100 mg/kg/day in 3 divided doses	Bidentate chelator — 3 molecules bind 1 Fe³⁺. Particularly effective at removing cardiac iron	Agranulocytosis (most serious — requires weekly CBC monitoring), arthropathy, GI upset	Best chelator for cardiac iron → often combined with DFO for severe cardiac siderosis
Deferasirox (DFX / Exjade / Jadenu)	Oral (once daily)	20–40 mg/kg/day (dispersible tablet) or 14–28 mg/kg/day (film-coated tablet)	Tridentate chelator — 2 molecules bind 1 Fe³⁺ → excreted mainly via faeces	GI upset, LFT derangement, renal impairment, hypotension, hypersensitivity ^[15]	Most convenient (once daily oral) → best compliance. Now first-line in many centres (TIF 2024 guidelines)

Key adjunct: Give Vitamin C to augment renal excretion of chelated iron, but do NOT give Vitamin C without deferoxamine, since Vitamin C alone increases iron absorption in the gut ^[3]^[4]. Vitamin C mobilises iron from stores and makes it available for chelation → synergistic when given with DFO. But without a chelator present, that mobilised iron causes more oxidative damage.

Keep the toxicity index (average daily dose ÷ serum ferritin) under 0.025 ^[17] — this prevents over-chelation, which can cause toxicity (ototoxicity, retinal damage) when iron stores are already low.

Serum ferritin level is useful as a screening tool in assessing iron balance but results may be inaccurate in predicting quantitative iron stores ^[3]^[4]. Quantitative liver iron and cardiac iron measurement by MRI is the standard indicator of total-body iron stores ^[3]^[4].

Modality	Frequency	Target
Serum ferritin	Every 3 months ^[17]	1000–2000 ng/mL
MRI T2 liver*	Annually (from ≥ 8 years old)	LIC 3–7 mg/g dry weight
Cardiac MRI T2*	Annually (from ≥ 8 years old) ^[17]	> 20 ms

4.4 Splenectomy

Splenectomy to decrease transfusion requirement in thalassaemia major ^[18]:

Increased transfusion requirement or cytopenias due to hypersplenism ^[17]
Symptomatic splenomegaly or other splenic complications (e.g. splenic infarction, splenic vein thrombosis) ^[17]

Generally deferred till ≥ 4 years old (often much later) ^[17] — but actually the effect on immunity is even worse at child age, so we try to delay it as much as possible ^[18]
In practice, many centres delay until ≥ 5–6 years

↓ anaemia, ↓ transfusion requirement (therefore ↓ iron overload), ↓ cytopenias, ↓ splenomegaly-related symptoms ^[17]

↑ Thromboembolism ^[17] — loss of splenic filtration → increased platelet count + circulating abnormal RBCs activate coagulation
↑ Life-threatening infection ^[17]^[18] — risk of infection from encapsulated bacteria → overwhelming post-splenectomy infection (OPSI) ^[18]
- Organisms: Streptococcus pneumoniae, Haemophilus influenzae type b, Neisseria meningitidis
- Must vaccinate before splenectomy (Pneumococcal, Hib, Meningococcal vaccines, ideally ≥ 2 weeks pre-op)
- Lifelong prophylactic penicillin (especially in children)
↑ Pulmonary hypertension ^[17]

Spurious leukocytosis, increased platelet counts, nucleated RBCs, Howell-Jolly bodies may appear on PBS post-splenectomy — these are expected findings, not pathological ^[18].

4.5 Curative Therapy — Allogeneic Haematopoietic Stem Cell Transplant (HSCT)

Allogeneic HSCT is a potentially curative treatment for those with severe disease ^[17].

NOT gold-standard yet (still transfusion ± chelation) due to numerous transplant-related complications ^[17]. However, outcomes have improved significantly, and HSCT is now the standard curative option for eligible patients, especially children.

Paediatric indications for allogeneic HSCT include thalassemia major ^[19]. The best outcomes are in:

Young children (< 14 years)
Low Pesaro risk class (minimal hepatomegaly, no portal fibrosis, adequate chelation)
HLA-matched sibling donor available

Presence of HLA-matched sibling: not common in HK ^[17] — with typical family sizes of 1–2 children, finding a matched sibling donor is difficult. Matched unrelated donors (MUD) and haploidentical transplants are increasingly used
HSCT-related risks: increased chance of rejection due to hyperplastic bone marrow ^[17] — the massively expanded thalassemic marrow is harder to ablate compared to leukaemia where the marrow is already replaced by disease
Graft-versus-Host Disease (GvHD): uncommon but can still occur ^[17]
Transplant-related mortality (TRM): ~5–10% in optimal settings with matched sibling donor

Myeloablative conditioning (e.g. busulfan + cyclophosphamide ± thiotepa) is used to ablate the patient's own hyperplastic marrow and allow engraftment of donor stem cells.

4.6 Gene Therapy and Novel Therapies

Betibeglogene autotemcel (beti-cel / Zynteglo) — approved by FDA (2022) and EMA for β-thal requiring regular transfusions
- Autologous CD34⁺ cells are harvested, transduced ex vivo with a lentiviral vector carrying a functional β-globin gene (βA-T87Q), then reinfused after myeloablative conditioning
- ~89% of patients become transfusion-independent in clinical trials
- Advantage: No donor needed (autologous), no GvHD risk
- Disadvantage: Requires myeloablative conditioning (risk of infertility, secondary malignancy), extremely expensive, limited long-term data

Exagamglogene autotemcel (exa-cel / Casgevy) — approved by FDA and EMA (2023) for β-thal and sickle cell disease
- Uses CRISPR-Cas9 to edit the BCL11A enhancer in autologous HSCs → reactivates foetal haemoglobin (HbF) production
- By increasing HbF, the imbalance between α and β chains is mitigated (γ-chains substitute for missing β-chains)
- Clinical trials show ~95% of patients become transfusion-free

SC luspatercept: newly approved for β-thalassemia major in 2019 ^[17]

Mechanism: Luspatercept is a recombinant fusion protein that acts as a TGF-β superfamily ligand trap — it binds and neutralises GDF11 and activin A, which normally inhibit late-stage erythropoiesis
By blocking these inhibitory signals → improves the quality (not just quantity) of erythropoiesis → reduces ineffective erythropoiesis → improves Hb
FDA/EMA approved for TDT (to reduce transfusion burden) and NTDT (to improve Hb)
This is NOT curative, but reduces transfusion requirements by ~30–50% in responders

In utero: May survive if active measures are taken (intrauterine transfusion) — serial intrauterine transfusions can keep the foetus alive
After birth: Transfusion dependent for life ^[2]
Curative: Allogeneic HSCT is the only definitive treatment
Prevention is the primary strategy: prenatal diagnosis (CVS/amniocentesis + DNA analysis) with option of pregnancy termination ^[4]

HbH disease management ^[15]:

Transfusion (especially during acute illness) — HbH disease patients can develop acute haemolytic crises during infections, fever, or exposure to oxidant drugs (similar to G6PD deficiency, because HbH is unstable and oxidant-sensitive)
Folic acid supplement ^[15]
Avoid oxidant drugs (though the list is less stringent than for G6PD)
Iron monitoring + chelation if iron overload develops
Splenectomy rarely needed (only if massive splenomegaly with hypersplenism)

Severity	Transfusion	Chelation	Folate	Splenectomy	HSCT / Gene Therapy	Genetic Counselling
Trait	No	No	No	No	No	Yes — essential
Intermedia / NTDT	Occasional (selected)	If iron overloaded	Yes (1–2 mg/d)	Rarely	Rarely	Yes
Major / TDT	Regular (q4 weeks)	Yes (from ≥ 3 yrs)	No (if on regular Tx)	If ↑Tx requirement	Yes (if eligible)	Yes
Hb Bart's	Lifelong (if survived)	Yes	N/A	N/A	Yes	Prevention = priority

High Yield Summary — Management of Thalassemia

Trait: Reassurance, genetic counselling, NO iron supplements unless documented concurrent IDA. Do not treat microcytosis with iron empirically.
Intermedia (NTDT): Folate 1–2 mg/day, low iron diet, occasional transfusion during crises/stress, iron monitoring.
Major (TDT): Regular transfusion programme q4 weeks, pre-transfusion Hb target 9.5–10.5 g/dL, post-transfusion Hb 14 g/dL (not > 15) ^[3]^[4].
Blood products: Leukodepleted, extended antigen matched (D, C, c, E, e, Kell), CMV-negative if HSCT candidate, newest bag ^[3]^[4]^[8].
Pre-medications: Chlorpheniramine 30 min before, Furosemide at start of transfusion ^[3]^[4].
Iron chelation starts: ≥ 3 years old, ferritin > 2000 ng/mL, or > 20 units transfused ^[3]^[4]^[17]. Three chelators: DFO (SC/IV), DFP (oral), DFX (oral). Target ferritin 1000–2000 ng/mL.
Vitamin C: Augments chelation but NEVER give without DFO (increases iron absorption alone) ^[3]^[4].
Splenectomy: Deferred till ≥ 4–6 years; for increasing transfusion requirements or symptomatic splenomegaly. Must vaccinate pre-op + lifelong penicillin prophylaxis.
HSCT: Curative, paediatric indication, NOT gold-standard yet ^[17]. Best with HLA-matched sibling donor.
Novel therapies: Gene therapy (beti-cel), gene editing (exa-cel / CRISPR), luspatercept (TGF-β trap reducing ineffective erythropoiesis).
Monitoring: Ferritin q3mo, MRI T2* liver + heart annually from ≥ 8 years, endocrine panel q6mo–yearly, infection screen, ophthalmology/audiology for chelation toxicity.

Active Recall - Thalassemia Management

References

^[2] Senior notes: Block A - Many members of the family have anaemia.pdf (Genetic counselling indications; ferritin rationale in intermedia; three indications for Hb study) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Blood transfusion goals, blood product specifications, pre-medications, iron chelation therapy, DFO dosing and side effects, chelation indications, monitoring) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Blood transfusion goals, blood product specifications, pre-medications, iron chelation therapy, DFO dosing and side effects, chelation indications, monitoring, prenatal diagnostic strategy) ^[6] Senior notes: Block A - Hematology Interactive Tutorial.pdf (Iron in blood = 250 mg per 500 mL; body cannot excrete iron; chelation agents DFO, DFP, deferasirox) ^[7] Senior notes: Block A - Polyuria and polydipsia_ glucose metabolism; diabetes mellitus; diabetic ketoacidosis.pdf (HbA1c unreliability in thalassemia) ^[8] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (Newest bag for thalassemia; delayed haemolytic transfusion reactions; MRI T2*; iron chelation types) ^[15] Senior notes: Maksim Medicine Notes.pdf (Thalassemia management summary; HbH disease management; chelation agents comparison; iron overload pathogenesis) ^[16] Senior notes: Adrian Lui Pediatrics Notes.pdf (Folate supplementation; low iron diet; regular transfusion indications; DNA-based genotyping) ^[17] Senior notes: Ryan Ho Haemtology.pdf (Comprehensive management — transfusion indications, chelation indications/targets/dosing, splenectomy timing/indications/risks, HSCT considerations, luspatercept, monitoring schedule) ^[18] Senior notes: Block A - Splenomegaly_ common causes of splenomegaly; myeloproliferative diseases.pdf (Splenectomy indications in thalassemia; OPSI risk; post-splenectomy CBC changes) ^[19] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (Paediatric indications for allogeneic HSCT including thalassemia major)

Complications of Thalassemia

The complications of thalassemia can be understood as flowing from three interconnected pathological streams — and every single complication traces back to one (or more) of these:

Chronic anaemia and ineffective erythropoiesis → bone marrow expansion, extramedullary haematopoiesis
Iron overload (from increased gut absorption + transfusion) → organ damage
Treatment-related → complications of chronic transfusion, splenectomy, chelation therapy

Think of it this way: the disease causes problems, and the treatment causes problems, and the two interact in a vicious cycle.

1. Iron Overload — The Major Killer

This is the single most important complication and the leading cause of morbidity and mortality in transfusion-dependent thalassemia (TDT). Understanding it from first principles makes every downstream complication intuitive.

Two sources ^[6]^[8]:

Increased gut iron absorption: Ineffective erythropoiesis → erythroid precursors secrete erythroferrone → suppresses hepcidin (the master iron regulatory hormone produced by the liver) → increased ferroportin expression on enterocytes and macrophages → more iron absorbed and released into plasma. This occurs even without transfusions (NTDT patients get iron-overloaded too)
Transfusion iron loading: 200 mg iron in 1 unit of blood ^[8]. A patient receiving 2 units every 4 weeks accumulates ~5,200 mg iron/year. Only 1 mg per day is excreted ^[8] — the body has no physiological mechanism to excrete excess iron ^[6]

Excess iron saturates transferrin → non-transferrin-bound iron (NTBI) appears in plasma → a particularly toxic subfraction called labile plasma iron (LPI) enters cells via non-specific uptake → catalyses the Fenton/Haber-Weiss reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + OH• + OH⁻) → generates reactive oxygen species (ROS) → oxidative damage to cell membranes, mitochondria, DNA → cell death and fibrosis ^[15].

Organ-Specific Iron Overload Complications

GC High Yield — Transfusion Haemosiderosis Case

A 31-year-old man with thalassemia major on lifelong regular transfusion with poor compliance to deferoxamine. Admitted with malaise and ankle oedema. Ferritin > 13,560 pmol/L, random sugar 25 mmol/L, CXR: cardiomegaly with CTR 0.7, echo EF 48% ^[14]. This case illustrates three simultaneous iron overload complications: cardiac (cardiomyopathy with heart failure), endocrine (diabetes mellitus), and hepatic (implied by massive ferritin).

Transfusion haemosiderosis — iron accumulation within the heart → heart failure ^[8]

Complication	Mechanism	Clinical Presentation
Iron-overload cardiomyopathy	NTBI enters cardiomyocytes via L-type calcium channels → ROS damage to myofibrils and mitochondria → cell death → replacement fibrosis → dilated cardiomyopathy	Progressive exertional dyspnoea, orthopnoea, PND, peripheral oedema, cardiomegaly on CXR, ↓ ejection fraction on echo ^[14]
Cardiac arrhythmias	Iron deposition disrupts cardiac conduction system and myocyte electrophysiology	Supraventricular tachycardia, atrial fibrillation, ventricular tachycardia (potentially fatal)
Pericarditis	Iron-mediated inflammation of pericardium	Chest pain, pericardial effusion (less common)

Why is the heart so vulnerable? The heart has limited regenerative capacity and very high metabolic demand (continuous aerobic metabolism). Iron-catalysed ROS are devastating to mitochondria-rich cardiomyocytes. Cardiac T2* < 10 ms on MRI signals severe cardiac iron and high imminent risk of heart failure/arrhythmia ^[17].

Monitoring: cardiac MRI T2 annually from ≥ 8 years old; target > 20 ms* ^[16]^[17]. Also ECG, echocardiography, MUGA scan.

Management: aggressive iron chelation (deferiprone particularly effective for cardiac iron removal ± combination with DFO); treat heart failure with standard HF therapy (diuretics, ACEi, beta-blockers once stabilised) ^[16].

Transfusion haemosiderosis — iron accumulation within the liver → liver fibrosis and HCC ^[8]

Complication	Mechanism
Hepatic fibrosis → Cirrhosis	Iron-mediated hepatocyte damage → stellate cell activation → collagen deposition → progressive fibrosis → cirrhosis
Hepatocellular carcinoma (HCC)	Chronic oxidative stress + cirrhosis → increased risk of malignant transformation
Chronic hepatitis (transfusion-transmitted)	Multiple transfusions → risk of HBV, HCV acquisition (now minimised by screening, but historically significant)

Monitoring: liver MRI T2 (for iron), LFT, USS hepatobiliary Q2 years for gallstones* ^[16], HCC screening by USS Q6 months if cirrhosis develops ^[16]. Infection screen Q6 months: HIV, HBV, HCV ^[16]^[17].

Transfusion haemosiderosis — iron accumulation within endocrine organs → diabetes mellitus, growth retardation, and hypogonadism ^[8]

The endocrine glands are exquisitely sensitive to iron toxicity because they are small, highly metabolically active, and have limited regenerative capacity.

Endocrine Complication	Mechanism	Monitoring
Hypogonadotropic hypogonadism	Iron deposition in the pituitary → destruction of gonadotroph cells → ↓ LH/FSH → ↓ testosterone/oestradiol ^[20]. This is the most common endocrine complication (~50–80% of inadequately chelated TDT patients)	LH, FSH, testosterone/oestradiol. Presents as secondary amenorrhoea, delayed/absent puberty, infertility, ↓ libido
Diabetes mellitus	Iron deposition in the pancreatic β-cells → oxidative damage → β-cell destruction → insulin deficiency ^[8]^[20]. Also contributes via hepatic insulin resistance from liver iron	BG/fructosamine/HbA1c Q6 months ^[16]^[17] — remember HbA1c is unreliable in thalassemia due to shortened RBC lifespan ^[7]
Hypothyroidism	Iron deposition in the thyroid gland → gland destruction → ↓ T3/T4	TFTs Q6 months ^[16]^[17]
Hypoparathyroidism	Iron deposition in the parathyroid glands → ↓ PTH → hypocalcaemia	Serum Ca/PO₄ Q6 months ^[16]^[17]. Presents as tetany, paraesthesia, Chvostek/Trousseau signs
Growth failure / Short stature	Iron damage to pituitary somatotrophs (↓ GH) + chronic anaemia + increased metabolic demands + hypogonadism (loss of pubertal growth spurt)	Height velocity, IGF-1, GH stimulation test
Adrenal insufficiency	Iron deposition in adrenal cortex (rare)	Cortisol, ACTH stimulation test

Thalassemia Major and Hypopituitarism

Secondary amenorrhoea due to hypogonadotropic hypogonadism, due to haemosiderosis of the pituitary. Haemosiderosis of the pancreas resulting in DM ^[20]. This is the classic exam vignette — a young thalassemia major patient with absent puberty, amenorrhoea, and elevated blood glucose. All three findings point to iron overload of endocrine organs. The hypogonadism is secondary (pituitary, NOT gonadal) — so LH/FSH are inappropriately low/normal ^[20], unlike primary gonadal failure (e.g. Turner syndrome, Klinefelter) where LH/FSH would be elevated.

Bronze skin pigmentation ("bronze diabetes" when co-existing with DM) — iron deposition in the dermis + increased melanin production stimulated by iron

These complications are most prominent when patients are inadequately transfused (pre-transfusion Hb frequently below target), allowing the bone marrow to remain in a state of massively expanded but ineffective erythropoiesis.

Complication	Mechanism	Clinical Features
Skeletal deformities / Thalassemic facies	Massive bone marrow expansion in the medullary cavities of flat bones → cortical thinning, widened diploic space → outward bowing of bone	Frontal bossing, maxillary hyperplasia, malar prominence, dental malocclusion, flat nasal bridge ("chipmunk facies") ^[3]^[4]. Skull XR: "hair-on-end" appearance
Pathological fractures / Osteoporosis	Marrow expansion thins cortical bone + iron toxicity to osteoblasts + endocrine dysfunction (hypogonadism → ↓ bone density, ↓ GH/IGF-1, hypoparathyroidism)	Vertebral compression fractures, long bone fractures, back pain. DEXA: ↓ BMD
Extramedullary haematopoiesis	The overwhelmed bone marrow recruits embryonic haematopoietic sites (liver, spleen) and can form haematopoietic tissue in unusual locations	Hepatosplenomegaly (most common); paravertebral masses (can cause spinal cord compression — a haematological emergency); pleural masses
Hypersplenism	Spleen enlarges from extramedullary haematopoiesis + chronic work of filtering abnormal RBCs → traps and destroys normal cells too → cytopenias beyond what the disease alone would cause	Increasing transfusion requirements, thrombocytopenia, neutropenia. This is the main indication for splenectomy
Growth failure	Chronic tissue hypoxia from anaemia + metabolic demands of expanded marrow divert energy from growth	Short stature, failure to thrive (paediatric)

Why Adequate Transfusion Prevents Skeletal Deformities

The hypertransfusion programme (keeping pre-transfusion Hb 9.5–10.5 g/dL) suppresses the patient's own erythropoiesis ^[3]^[4]. By suppressing the marrow drive, you prevent the downstream skeletal expansion, extramedullary haematopoiesis, and excessive iron absorption. This is why thalassemia major patients who are well-transfused from early childhood often have normal facial features, while those who present late or are under-transfused develop the classic thalassemic facies.

Regular transfusion benefits: ↓ hepatosplenomegaly, partially corrects abnormal skeletal development, short-term improvements in cardiac dilatation and systolic function ^[16].

Complication	Mechanism
Pigment (black) gallstones	Chronic haemolysis → ↑ unconjugated bilirubin → hepatic excretion of excess bilirubin into bile → supersaturation → precipitation of calcium bilirubinate → pigment stones. Monitoring: USS hepatobiliary Q2 years ^[16]
Jaundice	↑ Unconjugated bilirubin from haemolysis (pre-hepatic jaundice) — usually mild, constant
Leg ulcers	Chronic tissue hypoxia + abnormal RBC rheology → endothelial dysfunction → poor wound healing. More common in NTDT than TDT (paradoxically — because untransfused patients have more circulating abnormal RBCs and higher free Hb levels causing NO scavenging → vasoconstriction)
Pulmonary hypertension	Free Hb from haemolysis scavenges nitric oxide (NO) → reduced NO bioavailability → pulmonary vasoconstriction → vascular remodelling → pulmonary hypertension. Also: ↑ pulmonary HTN post-splenectomy ^[17] (unclear exact mechanism, possibly platelet-mediated)
Thromboembolism	Abnormal RBC membranes expose phosphatidylserine → procoagulant surface → hypercoagulable state. Also splenectomy → ↑ platelets + circulating abnormal RBCs. Risk of DVT, PE, portal vein thrombosis, stroke
Folate deficiency	High RBC turnover consumes folate → if not supplemented → megaloblastic change superimposed on microcytic anaemia (dimorphic picture)

4. Complications of Treatment

Thalassemia patients are especially prone to delayed haemolytic transfusion reactions ^[8]:

Minor blood group incompatibilities (e.g. Kidd antigen) — antibodies develop from repeated transfusion exposure, then wane. Re-exposure triggers an anamnestic immune response → haemolysis at 4–5 days post-transfusion ^[8]
Alloimmunisation — 10–30% of TDT patients develop alloantibodies, making future cross-matching increasingly difficult. This is why extended antigen matching (D, C, c, E, e, Kell) is mandatory ^[3]^[4]

Transfusion Complication	Mechanism
Febrile non-haemolytic transfusion reaction	Recipient antibodies against donor WBC antigens → cytokine release. Minimised by leukodepletion
Allergic/urticarial reaction	Recipient antibodies against donor plasma proteins
Transfusion-transmitted infections	HBV, HCV, HIV (historically significant; now minimised by NAT screening)
Iron overload (haemosiderosis)	Cumulative iron from chronic transfusions (see section 1)
TRALI (rare)	Donor anti-HLA/anti-neutrophil antibodies → pulmonary capillary leak
TACO (transfusion-associated circulatory overload)	Volume overload in patients with cardiac dysfunction

Infection screen Q6 months: HIV, HBV, HCV ^[16]^[17] — even with modern screening, chronic transfusion patients remain at cumulative risk and require ongoing viral surveillance.

Post-splenectomy complications ^[17]^[18]^[21]:

Complication	Mechanism	Prevention
Overwhelming post-splenectomy infection (OPSI)	Life-threatening infection from encapsulated bacteria ^[18] — S. pneumoniae, H. influenzae type b, N. meningitidis. The spleen is critical for opsonisation and clearance of encapsulated organisms	Pre-splenectomy vaccination (PCV13 + PPSV23, Hib, MenACWY, annual influenza) ^[21]; lifelong prophylactic penicillin (especially in children); patient education about fever
Thromboembolism	↑ Thromboembolism ^[17] — loss of splenic filtration → ↑ circulating platelets (reactive thrombocytosis) + abnormal RBCs with procoagulant membranes	Prophylactic aspirin if platelets > 1000 × 10⁹/L ^[21]; VTE prophylaxis
Pulmonary hypertension	↑ pHTN post-splenectomy ^[17] — multifactorial: platelet-mediated, NO scavenging, chronic thromboembolism	Echo surveillance
Reactive thrombocytosis	Loss of splenic pooling → release of sequestered platelets + thrombopoietin no longer cleared by spleen	Usually self-limiting; aspirin if extreme

Post-splenectomy CBC changes: spurious leukocytosis, increased platelet counts, Howell-Jolly bodies, nucleated RBCs ^[18] — these are expected findings, NOT indications for further workup.

Chelator	Side Effects	Monitoring
Deferoxamine (DFO)	Ototoxicity (sensorineural hearing loss), retinal damage (visual disturbance), bone dysplasia with truncal shortening ^[3]^[4]^[16]	Eyes and hearing assessment annually ^[16]^[17]; keep toxicity index < 0.025
Deferiprone (DFP)	Agranulocytosis (potentially fatal — must monitor), arthropathy, GI upset	Weekly CBC (absolute neutrophil count)
Deferasirox (DFX)	GI upset, LFT derangement, renal impairment, hypersensitivity	Monthly LFT, renal function; annual audiology

Serum zinc and copper monitoring annually ^[16]^[17] — chelation therapy can also chelate essential trace metals, leading to zinc and copper deficiency (causing immune dysfunction, growth impairment, skin changes).

When a mother carries a foetus with Hb Bart's hydrops fetalis:

50–60% chance of developing serious obstetric complications ^[4]:
- Pre-eclampsia (toxaemia of pregnancy)
- Post-partum haemorrhage (PPH)
- Obstructed labour (large hydropic foetus + massive placenta)
This is why prenatal diagnosis is indicated — not just for the foetus, but to protect the mother ^[4]

Often overlooked but critically important:

Chronic disease burden: Lifelong transfusions, chelation, clinic visits → impact on school/work, self-image
Body image concerns: Thalassemic facies (if under-transfused), short stature, delayed puberty, bronze skin
Depression/anxiety: Chronic illness, fertility concerns, fear of complications
Adherence challenges: DFO requires 8–12 hour SC infusions 5–7 nights/week → enormous compliance burden (this is the primary reason for poor chelation adherence)
Financial burden: Blood products, chelation, monitoring investigations — significant even in subsidised healthcare systems

Organ System	Complication	Primary Mechanism	Monitoring
Heart	Cardiomyopathy, arrhythmias, HF	Iron overload	Cardiac MRI T2, Echo, ECG annually*
Liver	Fibrosis, cirrhosis, HCC	Iron overload + viral hepatitis	Liver MRI T2, LFT, HBV/HCV screen, USS*
Endocrine	Hypogonadism, DM, hypothyroidism, hypoparathyroidism, GH deficiency	Iron overload → gland destruction	Ca/PO₄, TFTs, BG/fructosamine, LH/FSH, testosterone/oestradiol Q6 months
Skeleton	Thalassemic facies, osteoporosis, pathological fractures	Marrow expansion + iron toxicity + endocrinopathy	DEXA, clinical assessment
Hepatobiliary	Pigment gallstones	Chronic haemolysis → ↑ bilirubin	USS HBP Q2 years ^[16]
Vascular	Thromboembolism, pulmonary HTN	Haemolysis → NO scavenging; splenectomy; procoagulant RBCs	Echo (PHT), clinical vigilance
Infection	OPSI, transfusion-transmitted infections	Splenectomy; chronic transfusion	Vaccination, prophylactic penicillin, viral screen
Skin	Leg ulcers, bronze pigmentation	Tissue hypoxia + iron deposition	Clinical
Growth/Development	Growth failure, delayed puberty	Anaemia + iron overload + endocrinopathy	Height velocity, pubertal staging
Chelation toxicity	Ototoxicity, retinal damage, agranulocytosis, bone dysplasia	Drug side effects	Eyes, hearing, CBC (DFP), zinc/copper annually

High Yield Summary — Complications of Thalassemia

Iron overload is the #1 cause of death — cardiac (cardiomyopathy, arrhythmias), hepatic (fibrosis, cirrhosis, HCC), endocrine (hypogonadism, DM, hypothyroidism, hypoparathyroidism).
Iron sources: Increased gut absorption (hepcidin suppression) + transfusion loading (200 mg iron/unit, only 1 mg/day excreted) ^[6]^[8].
Iron deposits in: liver → fibrosis and HCC; endocrine organs → DM, growth retardation, hypogonadism; heart → heart failure ^[8].
Hypogonadism in thalassemia is secondary (pituitary iron deposition → hypogonadotropic hypogonadism with ↓ LH/FSH) ^[20].
Skeletal complications (thalassemic facies, osteoporosis) are prevented by adequate transfusion (suppresses marrow expansion).
Pigment gallstones from chronic haemolysis — monitor with USS Q2 years.
Transfusion complications: Alloimmunisation (→ delayed haemolytic transfusion reactions at 4–5 days), infection (HBV/HCV/HIV — screen Q6 months), iron overload.
Post-splenectomy: OPSI (encapsulated bacteria), thromboembolism, pulmonary HTN. Must vaccinate + prophylactic penicillin.
Chelation toxicity: DFO → ototoxicity, retinal damage; DFP → agranulocytosis; DFX → renal/hepatic impairment.
Obstetric: Hb Bart's hydrops fetalis → 50–60% maternal complication rate (pre-eclampsia, PPH).

Active Recall - Thalassemia Complications

References

^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (Blood transfusion goals and product specifications, chelation therapy side effects and indications) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Blood transfusion goals, chelation therapy, prenatal diagnostic strategy, obstetric complications of Hb Bart's) ^[6] Senior notes: Block A - Hematology Interactive Tutorial.pdf (Iron content in blood, body cannot excrete iron, chelation agents) ^[7] Senior notes: Block A - Polyuria and polydipsia_ glucose metabolism; diabetes mellitus; diabetic ketoacidosis.pdf (HbA1c unreliability in thalassemia) ^[8] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (Transfusion haemosiderosis — iron accumulation sites and consequences; delayed haemolytic transfusion reactions in thalassemia; 200 mg iron per unit; 1 mg/day excreted) ^[14] Lecture slides: Haematology Introduction to Haematological investigations (CBP, Clotting).pdf (Case 5 — thalassemia major patient with ferritin > 13560, random sugar 25, cardiomegaly, EF 48%) ^[15] Senior notes: Maksim Medicine Notes.pdf (Iron overload pathogenesis — Haber-Weiss reaction, NTBI) ^[16] Senior notes: Adrian Lui Pediatrics Notes.pdf (Monitoring schedule — pre-transfusion, Q6 months, Q1 year, Q2 years; cardiopulmonary management; HCC screening; chelation side effects) ^[17] Senior notes: Ryan Ho Haemtology.pdf (Monitoring schedule; splenectomy indications and risks — thromboembolism, life-threatening infection, pHTN; chelation targets; HSCT considerations) ^[18] Senior notes: Block A - Splenomegaly_ common causes of splenomegaly; myeloproliferative diseases.pdf (Splenectomy indications in thalassemia; OPSI risk from encapsulated bacteria; post-splenectomy CBC changes) ^[20] Senior notes: Block A - I keep on bumping into people on my side_ pituitary tumours; hypopituitarism.pdf (Thalassemia major and hypopituitarism — secondary amenorrhoea from hypogonadotropic hypogonadism due to pituitary haemosiderosis; DM from pancreatic haemosiderosis) ^[21] Senior notes: Maksim Surgery Notes.pdf (Splenectomy complications — OPSI pathogens, vaccination schedule, prophylactic aspirin if platelets > 1000)

High Yield Summary

Definition: Thalassemia = reduced rate of synthesis of globin chains (quantitative defect), NOT structural abnormality.
Epidemiology: Most common single-gene disorder worldwide. In HK: α-thal trait ~5%, β-thal trait ~3%, total carrier rate ~11.3%. Maintained by heterozygote advantage against malaria.
Genetics: α-globin = 4 gene copies (chr 16), β-globin = 2 gene copies (chr 11). α-thal usually deletions; β-thal usually point mutations. SEA deletion (cis) in HK = risk of Hb Bart's hydrops fetalis.
Pathophysiology: Globin chain imbalance → excess unpaired chains precipitate → (a) ineffective erythropoiesis (destruction in marrow) + (b) haemolysis (peripheral destruction in spleen). Unpaired α-chains (in β-thal) are MORE toxic than unpaired β-chains (in α-thal).
Iron overload from ↑ gut absorption (hepcidin suppression by erythroferrone) + transfusions. Heart is the #1 cause of death. Monitor with MRI T2*. Treat with chelation (DFO/DFP/DFX).
Clinical Classification: Major (transfusion-dependent) → Intermedia (moderate, not routinely transfusion-dependent) → Trait (mild/asymptomatic).
β-thal major presents at 3–6 months (after γ→β switch); Hb Bart's presents in utero (α-chains needed at all stages).
Thal trait vs IDA: Both microcytic. Thal trait = high RBC count, normal/mild ↓ Hb, normal iron studies. IDA = low RBC count, can be very low Hb, abnormal iron studies.
Pre-marital/prenatal counselling is critical in HK given high carrier rate. Three indications for Hb study: for the patient, for the carrier, for the unborn.
Thalassemia causes variable effects on HbA1c — unreliable for DM monitoring.

High Yield Summary — Differential Diagnosis of Thalassemia

Microcytic anaemia DDx (TAILS): Thalassemia, ACD, IDA, Lead poisoning, Sideroblastic anaemia. In HK, the two most common causes are IDA and thalassemia ^[9].
Thal trait vs IDA: Use RBC count (↑ in thal, ↓ in IDA), RDW (normal in thal, ↑ in IDA), iron studies (normal in thal, abnormal in IDA), HbA₂ (↑ in β-thal trait), blood smear (target cells + basophilic stippling in thal vs pencil cells in IDA) ^[2]^[9]^[13].
α-thal vs β-thal: HbA₂ ↑ in β-thal trait; HbH present in α-thal intermedia; DNA analysis needed for α-thal trait diagnosis.
Thalassemia vs haemoglobinopathy: Thalassemia = low MCV (quantitative); haemoglobinopathy = usually normal MCV (qualitative). "Not MCV — most haemoglobinopathies do not affect MCV" ^[2].
Reticulocyte count is inappropriately low in thalassemia major (ineffective erythropoiesis) — unlike other haemolytic anaemias where reticulocytes are high ^[3]^[4].
Always consider co-existing pathology when anaemia severity exceeds what thalassemia alone can explain ^[2].

High Yield Summary — Diagnosis of Thalassemia

Triggers: Low MCV +/- clinical features (pallor, splenomegaly, failure to thrive) ^[10]^[11].
Step 1 — CBC: Low MCV + high RBC count suggests thalassemia over IDA. Mentzer index < 13 → thalassemia; > 13 → IDA ^[6]^[9].
Step 2 — Iron studies: Normal iron studies excludes IDA and points towards thalassemia. Abnormal iron studies may indicate coexisting IDA (correct first, then reassess).
Step 3 — Hb study (HPLC/CE): HbA₂ ≥ 3.5% = β-thal trait. HbH detected = α-thal intermedia (HbH disease). Normal Hb study with persistent microcytosis → suspect α-thal trait → DNA analysis.
Step 4 — DNA analysis: Essential for α-thal trait confirmation, prenatal diagnosis, and genotyping for genetic counselling.
PBS features of thalassemia: hypochromia, microcytosis, target cells, basophilic stippling (distinguishing feature from IDA), teardrop cells, NRBCs.
Haemolysis screen: ↑ LDH, ↑ unconjugated bilirubin, ↓ haptoglobin, ↑ AST.
Iron overload monitoring: MRI T2 of liver and heart* (gold standard); serum ferritin (screening/trending).
Reticulocyte count is inappropriately low in β-thal major (ineffective erythropoiesis) despite severe anaemia.
Prenatal: CVS at 10–12 weeks or amniocentesis at 16–19 weeks with DNA analysis; serial USS for hydrops features.

High Yield Summary — Management of Thalassemia

Trait: Reassurance, genetic counselling, NO iron supplements unless documented concurrent IDA. Do not treat microcytosis with iron empirically.
Intermedia (NTDT): Folate 1–2 mg/day, low iron diet, occasional transfusion during crises/stress, iron monitoring.
Major (TDT): Regular transfusion programme q4 weeks, pre-transfusion Hb target 9.5–10.5 g/dL, post-transfusion Hb 14 g/dL (not > 15) ^[3]^[4].
Blood products: Leukodepleted, extended antigen matched (D, C, c, E, e, Kell), CMV-negative if HSCT candidate, newest bag ^[3]^[4]^[8].
Pre-medications: Chlorpheniramine 30 min before, Furosemide at start of transfusion ^[3]^[4].
Iron chelation starts: ≥ 3 years old, ferritin > 2000 ng/mL, or > 20 units transfused ^[3]^[4]^[17]. Three chelators: DFO (SC/IV), DFP (oral), DFX (oral). Target ferritin 1000–2000 ng/mL.
Vitamin C: Augments chelation but NEVER give without DFO (increases iron absorption alone) ^[3]^[4].
Splenectomy: Deferred till ≥ 4–6 years; for increasing transfusion requirements or symptomatic splenomegaly. Must vaccinate pre-op + lifelong penicillin prophylaxis.
HSCT: Curative, paediatric indication, NOT gold-standard yet ^[17]. Best with HLA-matched sibling donor.
Novel therapies: Gene therapy (beti-cel), gene editing (exa-cel / CRISPR), luspatercept (TGF-β trap reducing ineffective erythropoiesis).
Monitoring: Ferritin q3mo, MRI T2* liver + heart annually from ≥ 8 years, endocrine panel q6mo–yearly, infection screen, ophthalmology/audiology for chelation toxicity.

High Yield Summary — Complications of Thalassemia

Iron overload is the #1 cause of death — cardiac (cardiomyopathy, arrhythmias), hepatic (fibrosis, cirrhosis, HCC), endocrine (hypogonadism, DM, hypothyroidism, hypoparathyroidism).
Iron sources: Increased gut absorption (hepcidin suppression) + transfusion loading (200 mg iron/unit, only 1 mg/day excreted) ^[6]^[8].
Iron deposits in: liver → fibrosis and HCC; endocrine organs → DM, growth retardation, hypogonadism; heart → heart failure ^[8].
Hypogonadism in thalassemia is secondary (pituitary iron deposition → hypogonadotropic hypogonadism with ↓ LH/FSH) ^[20].
Skeletal complications (thalassemic facies, osteoporosis) are prevented by adequate transfusion (suppresses marrow expansion).
Pigment gallstones from chronic haemolysis — monitor with USS Q2 years.
Transfusion complications: Alloimmunisation (→ delayed haemolytic transfusion reactions at 4–5 days), infection (HBV/HCV/HIV — screen Q6 months), iron overload.
Post-splenectomy: OPSI (encapsulated bacteria), thromboembolism, pulmonary HTN. Must vaccinate + prophylactic penicillin.
Chelation toxicity: DFO → ototoxicity, retinal damage; DFP → agranulocytosis; DFX → renal/hepatic impairment.
Obstetric: Hb Bart's hydrops fetalis → 50–60% maternal complication rate (pre-eclampsia, PPH).

Thalassemia

1. Definition

2. Epidemiology

2.1 Global Epidemiology

2.2 Hong Kong Epidemiology

3. Risk Factors

4. Anatomy and Physiology of Normal Haemoglobin

4.1 Haemoglobin Structure

4.2 Globin Gene Organisation

4.3 Haemoglobin Switching

5. Etiology (Focus on Hong Kong)

5.1 α-Thalassemia

5.2 β-Thalassemia

5.3 δβ-Thalassemia and Hereditary Persistence of Foetal Haemoglobin (HPFH)

6. Pathophysiology

6.1 The Fundamental Problem: Globin Chain Imbalance

6.2 Consequences of Excess Unpaired Chains

In α-Thalassemia

In β-Thalassemia

6.3 The Two Cardinal Pathological Processes

A. Ineffective Erythropoiesis

B. Haemolysis (Peripheral Destruction)

6.4 Downstream Consequences of Ineffective Erythropoiesis

6.5 Iron Overload — The Major Killer

7. Classification

7.1 By Globin Chain Affected

7.2 By Clinical Severity (the Clinically Used Classification)

7.3 Modern Reclassification — Transfusion-Dependent vs Non-Transfusion-Dependent Thalassemia

8. Clinical Features

8.1 Organisation by Syndrome Severity

A. Thalassemia Trait / Minor (α-thal: 1–2 gene deletion; β-thal: heterozygous)

B. Thalassemia Intermedia (HbH disease / β-thal intermedia)

C. β-Thalassemia Major (Cooley's Anaemia)

D. Hb Bart's Hydrops Fetalis (α-Thal Major: --/--)

8.2 Key Symptoms and Their Pathophysiological Basis (Summary Table)

8.3 Differentiating Thalassemia Trait from Iron Deficiency Anaemia

9. Special Considerations

9.1 Pre-Marital and Prenatal Counselling

9.2 HbH/Constant Spring Disease

9.3 Interaction with Other Haemoglobinopathies

9.4 Iron Overload Monitoring

Active Recall - Thalassemia (Definition to Clinical Features)

References

Framing: What Are We Differentiating?

1. Differential Diagnosis of Microcytic Anaemia (MCV < 80 fL)

2. Differential Diagnosis of Haemolytic Anaemia

3. Differential Diagnosis Within Thalassemia Syndromes

α-Thalassemia vs β-Thalassemia

Distinguishing Thalassemia from Haemoglobinopathies

4. Diagnostic Algorithm — Approach to Microcytic Anaemia

5. Key Differentials in Specific Clinical Scenarios

Scenario A: Neonate with Severe Anaemia / Hydrops Fetalis

Scenario B: Infant (3–12 months) with Progressive Pallor and Failure to Thrive

Scenario C: Adult with Chronic Hypochromic Microcytic Anaemia

6. Impact on Other Investigations (Indirect Clues)

Active Recall - Thalassemia Differential Diagnosis

1. Diagnostic Criteria — Conceptual Framework

2. Stepwise Diagnostic Algorithm

3. Investigation Modalities — Detailed Interpretation

3.1 Complete Blood Count (CBC) with Red Cell Indices

3.2 Peripheral Blood Smear (PBS)

3.3 Iron Studies

3.4 Haemoglobin Study (HPLC / Capillary Electrophoresis)

3.5 Supravital Staining (HbH Inclusion Body Test)

3.6 Molecular / DNA Analysis

3.7 Evidence of Haemolysis — The Haemolysis Screen

3.8 Additional Investigations in Established Thalassemia

3.9 Prenatal and Neonatal Screening Investigations

4. Summary: Diagnostic Approach by Thalassemia Type

Active Recall - Thalassemia Diagnosis and Investigations

1. Management Overview — Organising Principles

2. Management of Thalassemia Trait (Minor)

3. Management of Thalassemia Intermedia (NTDT)

3.1 Supportive Measures

3.2 Occasional Transfusion

3.3 Iron Monitoring

4. Management of Thalassemia Major (TDT)

4.1 Regular Blood Transfusion — The Mainstay

Goals of Transfusion

Transfusion Interval