Haemolytic anaemias are those anaemias which result from an increase in the rate of destruction of circulating red cells, with a compensatory increase in production from bone marrow. ^[1]

Why this definition matters: The bone marrow is normal in haemolytic anaemia — the factory works fine, but the products (RBCs) are being destroyed too fast. This is fundamentally different from aplastic anaemia where the factory itself fails. The compensatory marrow response is why you see reticulocytosis — the marrow is pumping out young RBCs to compensate.

Two classification axes: (1) Hereditary vs Acquired; (2) Intrinsic vs Extrinsic ^[1]

Why two axes? Because "intrinsic" (defect is within the RBC itself) and "extrinsic" (something outside the RBC damages it) don't perfectly map onto inherited vs acquired. The important exception is PNH — it is an acquired intrinsic defect (a somatic mutation in the PIGA gene).

History: Family history, Ethnicity, Infection, Drugs, Transfusion history, Co-existing illnesses (autoimmune diseases, lymphoproliferative neoplasm), History of gallstones ^[1]

Examination: Pallor, Jaundice (no tea-coloured urine as in obstructive jaundice), Haemoglobinuria in intravascular haemolysis (e.g. PNH), Splenomegaly ^[1]

Why each matters — explained from first principles:

Anaemia (mildly macrocytic usually) with reticulocytosis ^[1]

Increased unconjugated bilirubin, LDH ^[1]

Reduced serum haptoglobin ^[1]

Increased methaemalbumin ^[1]

Blood film: Polychromasia, Spherocytes (HS, immune HA), RBC fragmentation (MAHA), RBC agglutination (cold agglutinin disease) ^[1]

Direct antiglobulin test (DAT/Coombs') — positive in immune haemolytic anaemia ^[1]

Why each lab finding occurs:

Due to autoimmune antibodies against self erythrocytes. Warm or cold auto-antibodies depending on the temperature at which the antibody binds better with erythrocytes (37°C vs 4°C). ^[1]

Blood count — increased reticulocyte. Blood film — microspherocytes. Increased bilirubin (unconjugated), LDH. Decreased haptoglobin, increased methaemalbumin. Specific test — Direct Antiglobulin Test (Direct Coombs' test). ^[1]

Why microspherocytes in AIHA? Antibody-coated RBCs pass through the spleen → macrophages nibble away at the membrane (partial phagocytosis) → RBC loses surface area but retains volume → spherical shape. These are microspherocytes because the membrane loss is progressive.

1. Transfusion if necessary ^[1] 2. Folate supplement ^[1] 3. Decrease further haemolysis: ^[1]

• Steroid or other immunosuppressants in autoimmune haemolytic anaemia
• Avoidance of certain drugs in drug-induced haemolytic anaemia
• Keep warm in cold haemagglutinin disease
• Splenectomy 4. Treat the underlying cause (e.g. AIHA due to underlying lymphoproliferative disorder) if necessary ^[1]

Why each treatment works:

• Transfusion: Life-saving if severely anaemic. Cross-matching can be difficult because autoantibodies react with all donor RBCs — the blood bank must do extended testing.
• Folate: Chronic haemolysis increases folate consumption (folate is needed for active erythropoiesis). Without supplementation, patients develop megaloblastic crisis on top of haemolysis.
• Steroids: Reduce autoantibody production + downregulate Fc receptor expression on macrophages → less phagocytosis of antibody-coated RBCs. First-line for warm AIHA.
• Avoid offending drugs: Self-explanatory in drug-induced cases.
• Keep warm: In cold AIHA, the antibodies bind at low temperatures → avoid cold exposure to prevent haemolytic episodes.
• Splenectomy: Removes the main site of extravascular haemolysis; more useful in warm AIHA where splenic macrophages are the primary destroyers.
• Treat underlying cause: If secondary to CLL or SLE, treating the primary disease may resolve the AIHA.

Pancytopenia resulting from bone marrow hypoplasia or aplasia ^[1]

Congenital vs acquired. Acquired: idiopathic vs secondary. ^[1]

Why is it called "aplastic"? The bone marrow becomes hypocellular ("aplastic" = without growth). Unlike haemolytic anaemia where the marrow is working overtime, here the marrow itself fails → all three lineages drop → pancytopenia (low RBCs, WBCs, and platelets).

Isolated aplasia of the erythroid series. Congenital: Diamond-Blackfan syndrome. Acquired: lymphoproliferative disease, thymoma, parvovirus B19. ^[1]

Why parvovirus B19? Parvovirus B19 has tropism for erythroid progenitor cells (it enters via the P antigen/globoside receptor on erythroid precursors). In a healthy person, this causes a transient drop in RBC production that goes unnoticed. But in patients with underlying chronic haemolysis (e.g. sickle cell, HS), the temporary halt in erythropoiesis precipitates a dramatic aplastic crisis because they depend on high marrow output to compensate for ongoing haemolysis.

Idiopathic — 70-80% ^[1]

Congenital: Fanconi anaemia, Shwachman-Diamond syndrome, Dyskeratosis congenita ^[1]

Drugs: Gold, Alcohol, Diclofenac acid, Indomethacin, Chloramphenicol, anti-convulsants ^[1]

Infection: non A,B,C hepatitis (sero-negative hepatitis) ^[1]

Environmental exposure: benzene, pesticide ^[1]

Expanded drug list from senior notes: ^[2][3]

• Cytotoxic drugs (anticipated, nadir day 7-10)
• Antibiotics: chloramphenicol, sulphonamide
• DMARDs: penicillamine, gold
• NSAIDs: phenylbutazone, indomethacin, diclofenac
• Thionamides: carbimazole, propylthiouracil
• Anticonvulsants: carbamazepine, phenytoin
• Alcohol
• Toxins: benzene, toluene (glue-sniffing)

Immune (T-cell) mediated suppression of marrow stem cells ^[1]

Why this matters for treatment: If the disease is driven by autoreactive T-cells attacking haematopoietic stem cells, then immunosuppressive therapy (ATG + cyclosporine) makes mechanistic sense — you're suppressing the T-cells that are destroying the marrow. This also explains why some patients respond to cyclosporine alone.

Symptoms of pancytopenia (anaemia, neutropenia, thrombocytopenia) ^[1]

NO lymphadenopathy. NO hepatosplenomegaly. ^[1]

In young patients, watch out for the presence of congenital physical abnormalities (inherited bone marrow failure syndromes) ^[1]

Why NO organomegaly? This is a crucial negative finding that distinguishes aplastic anaemia from leukaemia and lymphoproliferative disorders. In leukaemia, malignant cells infiltrate the spleen, liver, and lymph nodes → organomegaly. In aplastic anaemia, the marrow is simply empty — there are no proliferating cells to infiltrate organs.

Symptoms by lineage:

Blood count: pancytopenia; macrocytic anaemia; low reticulocyte count ^[1]

Blood film ^[1]

Autoimmune markers ^[1]

Vit B12 and folate levels ^[1]

Bone marrow: trephine biopsy is required for the assessment of cellularity ^[1]

Specialized tests: ^[1]

• Flow cytometry for CD55 and CD59 deficient RBC (to rule out PNH)
• Chromosome breakage with diepoxybutane (to screen for Fanconi anaemia)

Why each investigation:

Severe aplastic anaemia (SAA): ^[1]

• BM cellularity < 25%
• 2 out of 3:
  • Neutrophils < 0.5 × 10⁹/L
  • Platelets < 20 × 10⁹/L
  • Reticulocytes < 20 × 10⁹/L

Very severe aplastic anaemia: As for SAA but neutrophils < 0.2 × 10⁹/L ^[1]

Why these numbers matter: They determine treatment urgency. Very severe AA has the worst prognosis and requires the most aggressive therapy. The neutrophil count is the strongest prognostic factor — lower neutrophils = higher infection risk = higher mortality.

First line — allogeneic haematopoietic stem cell transplantation (for young patients with matched sibling donors) ^[1]

Anti-thymocyte globulin (ATG) + cyclosporine ^[1]

Cyclosporine A ^[1]

Supportive (blood products, iron chelation) ^[1]

Eltrombopag (high dose) + ATG and cyclosporine ^[1]

Treatment algorithm explained:

1. Young patient (< 40) + matched sibling donor → Allo-HSCT: This is curative. You replace the failed marrow with healthy donor stem cells. The younger the patient, the better they tolerate conditioning.

2. No matched sibling donor OR older patient → ATG + Cyclosporine: Since the pathogenesis is T-cell mediated, immunosuppression can allow the remaining stem cells to recover. ATG (anti-thymocyte globulin) directly depletes the offending T-cells. Cyclosporine maintains immunosuppression. Response rate ~60-70%.

3. Eltrombopag: A thrombopoietin receptor agonist. Initially used for thrombocytopenia, but high-dose eltrombopag has been shown to stimulate haematopoietic stem cell self-renewal across all lineages. Adding it to ATG + cyclosporine improves response rates. This is a newer addition to the treatment paradigm.

4. Supportive care: Red cell transfusions for symptomatic anaemia, platelet transfusions for bleeding, antibiotics/antifungals for infection. Iron chelation is needed because chronic transfusion leads to iron overload (no physiological mechanism to excrete excess iron → deposits in heart, liver, endocrine organs). ^[6]

Four pathophysiological categories: ^[1]

1. Inherited bone marrow failure syndromes → pancytopenia
2. Disorders of red cell membrane
3. Disorders of haemoglobin (haemoglobinopathy and thalassaemia)
4. Disorders of RBC metabolism

Think of the RBC as a bag of haemoglobin wrapped in a membrane powered by metabolism. Any component can be defective:

• Membrane defects → cells are abnormally shaped → trapped and destroyed in spleen
• Haemoglobin defects → abnormal or reduced globin chains → haemolysis or ineffective erythropoiesis
• Enzyme defects → inability to generate energy or handle oxidative stress → haemolysis

Family history – pattern of inheritance, Age of onset, Drug history, Symptoms of haemolysis, Transfusion requirement, Complications (including those due to long-term red cell transfusion) ^[1][2]

Pallor, Jaundice, Splenomegaly, Skin complexion, Skeletal deformities ^[1][2]

Why skeletal deformities? In severe congenital anaemias (e.g. thalassaemia major, Fanconi anaemia), marrow expansion to compensate for ineffective erythropoiesis causes bony changes — frontal bossing, maxillary hyperplasia ("chipmunk face"), thinning of cortical bone. In Fanconi, the deformities are developmental (thumb/radius anomalies).

^[1]

Understanding vertical vs horizontal interactions:

• Vertical interactions (ankyrin, band 3, protein 4.2) anchor the cytoskeleton to the lipid bilayer. Defects → membrane loss (vesiculation) → spherocytosis
• Horizontal interactions (spectrin-spectrin, spectrin-actin via protein 4.1) maintain the structural integrity of the cytoskeleton lattice. Defects → membrane fragmentation → elliptocytosis or poikilocytosis

Presence of spherocytes, Haemolytic anaemia — mild to severe, Autosomal dominant ^[1]

60% result from a defect in the ankyrin-spectrin complex or vertical interaction ^[1]

Clinical features: Jaundice (indirect hyperbilirubinaemia), Splenomegaly, Gallstones, Aplastic crisis — primary parvovirus B19 infection ^[1]

Extravascular haemolysis, Blood film — spherocytes, MCHC is often raised ^[1]

Osmotic fragility test, Eosin-5-maleimide (EMA) binding (decreased binding in HS) ^[1]

Pathophysiology explained step by step:

1. Mutation in vertical interaction proteins (ankyrin, spectrin, band 3) → weakened anchoring of lipid bilayer to cytoskeleton
2. Membrane undergoes microvesiculation — small blebs of lipid bilayer pinch off
3. RBC loses surface area but retains intracellular volume → surface-area-to-volume ratio decreases → cell becomes spherical
4. Spherocytes are less deformable → cannot squeeze through the narrow splenic sinusoids (3μm slits)
5. Trapped spherocytes → phagocytosed by splenic macrophages → extravascular haemolysis

Why MCHC is raised: The cell has lost membrane (volume stays same or slightly less, Hb content stays same) → same Hb concentrated in a smaller package → MCHC goes up. This is one of the few conditions where MCHC > 36 g/dL. ^[4]

Why EMA binding is decreased: EMA binds to band 3 protein on the RBC surface. In HS, there is reduced band 3 (or reduced membrane in general) → less EMA binding → detectable by flow cytometry. This is now the preferred diagnostic test over osmotic fragility. ^[1][4]

Why osmotic fragility is increased: Spherocytes have reduced surface-area-to-volume ratio → less room to swell before bursting. When placed in hypotonic solution, they lyse earlier than normal biconcave RBCs.

Treatment: Folic acid supplement, Compensated haemolysis — no specific treatment, Cholecystectomy if symptomatic gallstones, Splenectomy in severe haemolysis ^[1]

Why splenectomy works in HS: The spleen is the site of destruction. Remove the executioner → RBCs survive longer. Spherocytes persist after splenectomy (the membrane defect remains), but they are no longer destroyed prematurely. Post-splenectomy vaccination (pneumococcal, meningococcal, Haemophilus) is essential due to overwhelming post-splenectomy infection (OPSI) risk.

G6PD deficiency, Pyruvate kinase deficiency, Deficiency of other glycolytic pathway enzymes → Congenital non-spherocytic haemolytic anaemia ^[1]

The lecture slide shows the glycolytic pathway and pentose phosphate shunt diagram. ^[1]

Why these pathways matter for RBCs: Mature RBCs have no mitochondria → they rely entirely on anaerobic glycolysis (Embden-Meyerhof pathway) for ATP and on the pentose phosphate shunt (hexose monophosphate shunt) for NADPH to combat oxidative stress.

• Glycolysis → ATP (maintains cation pumps, membrane integrity) + 2,3-DPG (regulates O₂ affinity)
• Pentose phosphate shunt → NADPH (reduces glutathione via glutathione reductase → reduced glutathione protects Hb and membrane from oxidative damage)

X-linked recessive. Incidence in HK: 4.5% in males and 0.5% in females ^[1]

More than 100 variants associated with enzyme deficiency. Type B refers to the wild-type ^[1]

Why X-linked matters clinically: Males are hemizygous (one X chromosome) → if they inherit the defective gene, they are fully affected. Females are usually carriers (heterozygous) → generally protected by their normal X chromosome. However, due to lyonization (random X-inactivation), some female carriers can have a proportion of G6PD-deficient RBCs and may be mildly affected.

^[1]

Intravascular haemolysis with haemoglobinuria — acute or chronic (not common) ^[1]

Precipitated by infection or acute medical illness, drugs and Fava beans ^[1]

Drugs: sulphonamides, rasburicase, primaquine ^[1]

Why G6PD-deficient RBCs are vulnerable to oxidative stress:

1. G6PD is the rate-limiting enzyme of the pentose phosphate shunt
2. G6PD generates NADPH → needed to regenerate reduced glutathione (GSH) via glutathione reductase
3. GSH protects Hb and RBC membranes from reactive oxygen species (ROS)
4. Without adequate G6PD → ↓NADPH → ↓GSH → Hb precipitates as Heinz bodies → membrane damage → intravascular haemolysis
5. Triggers (infection, drugs, fava beans) increase ROS production → overwhelm the already impaired antioxidant system

Common triggers (mnemonic: "FIDAS"): Fava beans, Infection, Drugs (sulphonamides, primaquine, rasburicase, dapsone, nitrofurantoin), Acidosis, Stress

Blood film — polychromasia, ghost or hemi-ghost cells ^[1]

G6PD assay — may be normal during the acute phase as young red cells and reticulocytes may have normal G6PD levels ^[1]

Blood film findings explained:

• Polychromasia: Reticulocytosis (compensatory)
• Ghost/hemi-ghost cells: Damaged RBCs that have partially lost their haemoglobin content — the Hb has precipitated or leaked out, leaving a "ghost" outline
• Heinz bodies (seen with supravital staining): Denatured, precipitated Hb within RBCs
• Bite cells: Splenic macrophages remove Heinz bodies by "pitting" → creates indentations in the RBC

Supportive. Blood transfusion. Folic acid. Stop and avoid offending agents. ^[1]

The most important management is PREVENTION: Give patients a list of drugs and foods to avoid. In HK, newborn screening identifies G6PD-deficient babies → parents are counselled.

1. A 25-year-old Chinese male presents with acute jaundice and dark urine after taking a course of co-trimoxazole for UTI. His G6PD assay returns normal. What is the MOST APPROPRIATE next step? → Repeat G6PD assay in 2-3 months (falsely normal during acute phase due to selective destruction of older, more deficient RBCs and compensatory reticulocytosis)

2. A 3-year-old girl with hereditary spherocytosis presents with sudden severe anaemia and a reticulocyte count of 0.1%. What is the MOST LIKELY cause? → Parvovirus B19 aplastic crisis (tropism for erythroid progenitors → temporary halt in RBC production → catastrophic drop in Hb in patients dependent on high marrow output)

3. A 20-year-old with pancytopenia, no organomegaly, and hypocellular BM trephine. Which investigation would you request to exclude PNH? → Flow cytometry for CD55 and CD59 deficient cells

4. Which of the following is the first-line treatment for a 15-year-old with severe aplastic anaemia who has a matched sibling donor? → Allogeneic haematopoietic stem cell transplantation

5. In warm AIHA, what is the predominant antibody class and what does DAT show? → IgG; DAT positive for IgG ± C3d

6. A patient with cold AIHA secondary to Mycoplasma pneumoniae. What is the most important non-pharmacological advice? → Keep warm / avoid cold exposure

7. A couple are both alpha-thalassaemia carriers. What prenatal investigation should be offered? → Chorionic villus sampling or amniocentesis for DNA analysis to exclude Hb Bart's hydrops fetalis

1. "A 10-year-old boy is found to have pancytopenia, short stature, and absent thumbs bilaterally. Name the most likely diagnosis and the confirmatory test." → Fanconi anaemia; DEB chromosome breakage test

2. "List 4 causes of acquired aplastic anaemia." → Idiopathic (immune-mediated), drugs (chloramphenicol, anticonvulsants), sero-negative hepatitis, environmental toxins (benzene)

3. "Compare warm and cold AIHA in terms of antibody class, secondary causes, and key management difference." → See table in section 2.1