Non-megaloblastic anaemia is a form of macrocytic anaemia in which large red blood cells occur without the hypersegmented neutrophils or abnormal nuclear maturation seen in megaloblastic anaemia, typically caused by conditions such as liver disease, hypothyroidism, alcoholism, or myelodysplastic syndromes.

Non-Megaloblastic Anaemia

The epidemiology of non-megaloblastic anaemia mirrors that of its underlying causes. Since this is a heterogeneous group, let's frame it by the most common aetiologies:

Aetiology	Epidemiological Profile
Alcoholism (most common cause overall) ^[1]	Extremely common in Hong Kong; heavy drinkers, especially those with concurrent liver disease
Liver disease (chronic) ^[3]^[4]	Common in HK due to high prevalence of chronic hepatitis B (8% carrier rate historically) → cirrhosis; also alcoholic liver disease and NAFLD/MASLD (rising)
Hypothyroidism ^[1]	More common in women; prevalence ~2-5% of adult females
Haemolytic anaemia (with reticulocytosis) ^[1]^[3]^[4]	Varies by cause; in HK, G6PD deficiency is prevalent (~4.5% of males), autoimmune haemolytic anaemia (AIHA) less common
Aplastic anaemia ^[3]^[4]^[5]	Incidence 2-3× higher in East Asia compared to the West (~5-7/million/year in Asia vs 2/million/year in Europe); peak bimodal: young adults (15-25y) and elderly (> 60y)
Myelodysplastic syndrome (MDS) ^[1]^[3]^[4]	Median age ~65 years; M > F; incidence increases with age
Drugs (e.g., azathioprine, methotrexate, hydroxyurea)	Iatrogenic; common in patients on immunosuppression or cytoreductive therapy

Risk factors (Hong Kong focus):

Chronic alcohol use → direct toxic effect on erythroid membrane lipid metabolism + associated liver disease
Chronic hepatitis B/C → cirrhosis → altered lipoprotein metabolism → excess cholesterol deposited in RBC membranes
Hypothyroidism → especially in women, post-thyroidectomy, or autoimmune thyroiditis
G6PD deficiency → common in Southern Chinese males; causes episodic haemolysis with reticulocytosis (reticulocytes are larger → raises MCV)
Haematological malignancy → MDS more common in elderly, prior chemotherapy/radiation exposure
Medication use → immunosuppressants (methotrexate, azathioprine), antiretrovirals (zidovudine/AZT), hydroxyurea

3. Anatomy and Function: The Red Blood Cell Membrane

Understanding why non-megaloblastic macrocytosis occurs requires understanding normal RBC membrane architecture:

4. Aetiology (Hong Kong Focus) and Pathophysiology

GC Exam Framing – Non-Megaloblastic Macrocytic Anaemia Causes

From GC 097 and the Pallor lecture slides, the non-megaloblastic macrocytic causes explicitly listed are: alcoholism (most common), liver disease, hypothyroidism, haemolytic anaemia (due to reticulocytosis), aplastic anaemia, and myelodysplastic syndrome. ^[1]^[3]^[4]

Cause	Pathophysiological Mechanism
Drugs (methotrexate, azathioprine, 6-MP, hydroxyurea, zidovudine/AZT, TKIs like imatinib)	Interfere with DNA synthesis (similar to megaloblastic mechanism) → some classify drug-induced causes under megaloblastic ^[1]; however, the PBS may show round macrocytes without classic hypersegmentation → overlap category
Pregnancy	Physiological haemodilution + increased erythropoiesis with reticulocytosis; also increased folate demand (can become truly megaloblastic if folate not supplemented)
Smoking	Mild macrocytosis; mechanism unclear — possibly carboxyhaemoglobin shifts oxygen-dissociation curve → compensatory erythropoiesis
Multiple myeloma / paraproteinaemia	RBC rouleaux formation can artefactually increase MCV on automated counters; also associated marrow infiltration
Post-splenectomy	Spleen normally culls larger and abnormal RBCs → after splenectomy, larger cells persist in circulation

Common Exam Pitfall

Do NOT confuse drug-induced macrocytosis (e.g., from methotrexate or azathioprine) as always being "non-megaloblastic." These drugs inhibit DNA synthesis and can cause a megaloblastic picture with hypersegmented neutrophils. The distinction depends on the PBS morphology. If in doubt, check for hypersegmented neutrophils and B12/folate levels. The GC lecture slide lists immunosuppressants (MTX/AZA) and TKIs under megaloblastic causes ^[1].

Non-megaloblastic anaemia can be classified by the underlying mechanism:

Key distinction table from Maksim Medicine Notes ^[1]:

Feature	Megaloblastic	Non-Megaloblastic
Pathophysiology	Nuclear-cytoplasmic maturation asynchrony	Membrane abnormalities with abnormal cholesterol metabolism
Aetiology	B12 deficiency, Folate deficiency, Drugs (MTX/AZA, TKIs)	Alcoholism (MC), Liver disease, Hypothyroidism, Haemolytic anaemia (reticulocytosis), Aplastic anaemia, MDS
PBS	Oval macrocytes, Hypersegmented neutrophils	Round macrocytes, Normal neutrophils
Investigations	Active B12 and folate levels ± RBC folate	Haemolytic screen (LDH, haptoglobin, bilirubin, reticulocyte), LFT, TFT

6. Clinical Features

The clinical features of non-megaloblastic anaemia depend on:

The anaemia itself (common to all anaemias)
The underlying cause (specific features)

6.1 Symptoms

Symptom	Pathophysiological Basis
Fatigue / lethargy	Reduced oxygen-carrying capacity → tissue hypoxia → reduced ATP generation in muscles and CNS
Dyspnoea on exertion	Decreased O₂ delivery to exercising muscles → compensatory increased respiratory rate and depth
Palpitations	Compensatory increased cardiac output (via increased heart rate and stroke volume) to maintain oxygen delivery despite low Hb
Dizziness / light-headedness	Cerebral hypoperfusion with reduced O₂, especially on standing (postural)
Headache	Cerebral vasodilation as a compensatory response to hypoxia
Angina pectoris	In patients with pre-existing coronary artery disease, reduced O₂ delivery precipitates myocardial ischaemia
Claudication	Similar mechanism in peripheral arteries → leg muscle ischaemia on walking
Syncope	Severe anaemia → cardiovascular decompensation → reduced cerebral perfusion

Cause	Specific Symptoms	Pathophysiological Basis
Alcoholism	History of heavy alcohol intake, nausea, anorexia, memory lapses, withdrawal symptoms	Direct neurotoxicity of ethanol; GI mucosal irritation; thiamine deficiency
Liver disease	Abdominal distension (ascites), easy bruising, pruritus (cholestasis), leg swelling	Portal hypertension → ascites; impaired clotting factor synthesis → coagulopathy; bile salt deposition in skin → itch
Hypothyroidism	Cold intolerance, weight gain, constipation, dry skin, menorrhagia, cognitive slowing, depressed mood	Reduced basal metabolic rate → less heat generation; decreased GI motility; reduced sympathetic tone; altered HPO axis
Haemolytic anaemia	Dark urine (cola-coloured in intravascular haemolysis), jaundice, episodic crises (in G6PD after trigger exposure), back/abdominal pain during crises	Haemoglobinuria from free Hb in urine; unconjugated hyperbilirubinaemia; free Hb and breakdown products cause renal/mesenteric vasoconstriction
Aplastic anaemia	Recurrent infections, mucosal bleeding, petechiae/bruising, fatigue	Neutropenia → infections; thrombocytopenia → bleeding; anaemia → fatigue
MDS	Often insidious fatigue, recurrent infections, easy bruising; typically in elderly	Progressive trilineage failure; ineffective haematopoiesis

6.2 Signs

Sign	Pathophysiological Basis
Pallor (conjunctival, palmar creases, nail beds)	Reduced Hb → less oxyHb → less red colouration of perfused tissues; conjunctival pallor is most reliable
Tachycardia	Compensatory increased heart rate to maintain cardiac output (CO = HR × SV)
Hyperdynamic circulation: bounding pulse, systolic flow murmur, wide pulse pressure	Low viscosity blood + high CO → turbulent flow across valves; reduced peripheral resistance
Postural hypotension	If acute/severe → reduced intravascular volume/compensatory mechanisms overwhelmed
Cardiac failure signs (in severe/chronic anaemia): raised JVP, peripheral oedema, bibasal crepitations	High-output cardiac failure — the heart cannot sustain the increased workload chronically; especially in elderly with pre-existing cardiac disease

Cause	Specific Signs	Pathophysiological Basis
Alcoholism	Dupuytren's contracture, spider naevi, gynaecomastia, parotid enlargement, hepatomegaly (early) or shrunken liver (late cirrhosis), tremor, peripheral neuropathy	Palmar fibromatosis from collagen deposition; oestrogen excess from impaired hepatic metabolism; ethanol neurotoxicity
Liver disease	Jaundice, spider naevi (> 5 pathological), palmar erythema, caput medusae, ascites, splenomegaly, leuconychia, flapping tremor (asterixis in encephalopathy)	Bilirubin accumulation; arteriolar dilation from oestrogen/nitric oxide excess; portal hypertension → collaterals, ascites, splenomegaly; hypoalbuminaemia
Hypothyroidism	Bradycardia, dry coarse skin, non-pitting oedema (myxoedema), periorbital puffiness, delayed relaxation of ankle jerks, goitre (if Hashimoto's), coarse hair, lateral eyebrow thinning	Reduced sympathetic tone → bradycardia; mucopolysaccharide/hyaluronic acid deposition in dermis → myxoedema; reduced metabolic activity of hair follicles
Haemolytic anaemia	Jaundice (lemon-yellow), splenomegaly (extravascular haemolysis), dark urine, leg ulcers (chronic haemolysis, especially sickle cell), gallstones (pigmented)	Unconjugated bilirubin from Hb breakdown; reticuloendothelial system hyperplasia → splenomegaly; chronic haemolysis → excess bilirubin → pigment gallstones; microvascular occlusion → skin ulcers
Aplastic anaemia	Petechiae, ecchymoses, mucosal bleeding (gum, nose), signs of infection (fever, oral ulcers, pneumonia), NO splenomegaly (because marrow is empty, not infiltrated)	Thrombocytopenia → petechial bleeding; neutropenia → infections; pancytopenia in the absence of extramedullary haematopoiesis → no organomegaly
MDS	Often minimal signs beyond pallor; NO hepatosplenomegaly ^[7]; may have signs of infection or bleeding	Ineffective haematopoiesis confined to marrow; no extramedullary haematopoiesis (distinguishes from MPN)

Clinical Pearl – Distinguishing MDS from MPN on Examination

MDS has NO hepatosplenomegaly ^[7], while myeloproliferative neoplasms (MPN) characteristically cause splenomegaly (often massive in myelofibrosis or CML). This is a high-yield distinguishing feature on clinical examination.

Finding on PBS	Suggests
Round macrocytes, target cells	Liver disease, alcoholism
Polychromasia (reticulocytes)	Haemolytic anaemia, acute blood loss recovery
Dimorphic picture (both macrocytes and microcytes → high RDW)	Combined deficiency (e.g., iron + B12/folate), sideroblastic anaemia, post-transfusion
Acanthocytes (spur cells)	Severe liver disease (spur cell anaemia)
Pseudo-Pelger-Huët neutrophils (bilobed)	MDS
Nucleated RBCs (without severe anaemia)	Myelophthisis (marrow infiltration), MDS
Tear-drop cells (dacrocytes)	Myelofibrosis, marrow infiltration
Pancytopenia with normal morphology	Aplastic anaemia

8. Special Topics Relevant to Non-Megaloblastic Anaemia

Luspatercept (Reblozyl) is a specific activin receptor fusion protein that acts as a ligand trap to neutralize negative regulators of late-stage erythropoiesis ^[9].
In MDS, the SMAD2/3 signalling pathway (part of the TGF-β superfamily) is constitutively activated and overexpressed in CD34+ cells → inhibits terminal erythroid differentiation → anaemia ^[9].
Luspatercept binds these TGF-β superfamily ligands before they can activate SMAD2/3, thereby releasing the brake on late-stage erythroid maturation and reducing transfusion dependence.
Approved for transfusion-dependent anaemia in MDS with ring sideroblasts.

High Yield Summary

Non-Megaloblastic Macrocytic Anaemia — Key Points:

Definition: Macrocytic anaemia (MCV > 100 fL) NOT caused by B12/folate deficiency or impaired DNA synthesis. Caused by membrane lipid abnormalities, reticulocytosis, or marrow failure/dysplasia.
PBS hallmark: Round macrocytes with normal neutrophils (vs. oval macrocytes + hypersegmented neutrophils in megaloblastic).
Most common cause: Alcoholism — direct toxic effect on erythroid membrane + altered lipid metabolism ± associated liver disease.
Main causes (exam list): Alcoholism, liver disease, hypothyroidism, haemolytic anaemia (reticulocytosis), aplastic anaemia, MDS.
Aplastic anaemia: Pancytopenia from BM hypoplasia; 70-80% idiopathic (T-cell mediated); hepatitis is a well-known preceding infection; BM biopsy shows hypocellular marrow with > 90% fat.
MDS: Clonal dysplastic haematopoiesis; median age ~65; may transform to AML; NO hepatosplenomegaly.
Investigation approach: PBS morphology → reticulocyte count → if high: haemolytic screen; if low/normal: LFT, TFT, alcohol history → if all normal: bone marrow biopsy (for aplastic anaemia or MDS).
Pathophysiology of membrane-mediated macrocytosis: Excess free cholesterol from dysregulated lipoprotein metabolism → deposits into RBC membrane → increases surface area → round macrocytes.

Active Recall – Non-Megaloblastic Anaemia

Differential Diagnosis of Non-Megaloblastic Macrocytic Anaemia

When a patient presents with macrocytic anaemia (MCV > 100 fL) and the peripheral blood smear shows round macrocytes with normal neutrophils (i.e., no oval macrocytes, no hypersegmented neutrophils), you have established that you are dealing with a non-megaloblastic picture ^[1]. The next challenge is determining which non-megaloblastic cause is responsible. But before you can do that, you must first confidently exclude megaloblastic causes — because the clinical consequences of missing B12 deficiency (e.g., subacute combined degeneration of the cord) are devastating and the treatment is simple.

The differential diagnosis therefore operates at two levels:

Level 1 — Is this truly non-megaloblastic? (i.e., exclude megaloblastic anaemia)
Level 2 — Among the non-megaloblastic causes, which one is it?

Before attributing macrocytosis to a non-megaloblastic cause, you must exclude B12 and folate deficiency. This is not just academic — it is a patient safety imperative.

Why Must You Exclude Megaloblastic Anaemia First?

B12 deficiency can cause irreversible neurological damage (subacute combined degeneration of the cord) even before haematological changes become apparent ^[10]. Neurons require higher B12 levels to function than the bone marrow does, so neuropsychiatric symptoms can present in the absence of haematological changes ^[10]. Missing this diagnosis has medicolegal and patient-safety implications. Always check B12 and folate levels in ANY macrocytic anaemia.

Key differentiating features — Megaloblastic vs Non-Megaloblastic:

Feature	Megaloblastic	Non-Megaloblastic
PBS morphology	Oval macrocytes + hypersegmented neutrophils (≥ 5% with 5 lobes or ≥ 1% with ≥ 6 lobes) ^[1]^[11]	Round macrocytes + normal neutrophils ^[1]
Degree of macrocytosis	Often severe (MCV > 110-115 fL); MCV > 120 fL almost exclusively megaloblastic or chemotherapy ^[12]^[13]	Usually mild-moderate (MCV 100-110 fL)
Other cytopenias	Pancytopenia common (all rapidly dividing cells affected) ^[12]	Variable — depends on cause (pancytopenia in aplastic anaemia/MDS; isolated anaemia in liver disease/hypothyroidism)
Reticulocyte count	Low (ineffective erythropoiesis → intramedullary haemolysis) ^[12]	Variable — high in haemolysis, low in marrow failure
Neurological features	Subacute combined degeneration of cord (B12 only) ^[10] — impaired vibration/proprioception, paraparesis	Absent (unless from the underlying cause, e.g., peripheral neuropathy from alcohol)
Serum B12 / folate	Low active B12 (holotranscobalamin) and/or low folate ^[1]	Normal
Intramedullary haemolysis markers	Elevated unconjugated bilirubin + LDH, low haptoglobin (from destruction of megaloblastic precursors within BM) ^[12]	Present only if there is concurrent haemolysis (peripheral, not intramedullary)

A MCV of greater than 120 fL generally only has 2 differentials: chemotherapy or pernicious anaemia ^[12]. This is a high-yield clinical pearl — if you see extreme macrocytosis, think megaloblastic first.

Why the distinction matters clinically:

If megaloblastic → treat the deficiency (parenteral B12 for pernicious anaemia, oral folate for folate deficiency) and the anaemia corrects
If non-megaloblastic → treating with B12/folate will NOT help; you must find and address the underlying cause

Level 2: Differential Diagnosis Among Non-Megaloblastic Causes

Once you have confirmed normal B12 and folate levels, PBS showing round macrocytes without hypersegmented neutrophils, the differential narrows to the non-megaloblastic causes. The reticulocyte count is the single most important next step to bifurcate the differential:

Let us now systematically go through each differential, explaining why each cause produces macrocytosis, what clinical clues point towards it, and how to distinguish it from the others.

Why does it cause macrocytosis? Compensatory reticulocytosis — reticulocytes are 20-25% larger than mature RBCs, so a high reticulocyte count raises the MCV.

Clinical clues:

Pallor, jaundice (without tea-coloured urine in extravascular haemolysis), splenomegaly ^[14]
Hemoglobinuria (coca-cola urine) suggests intravascular haemolysis — top 2 differentials: paroxysmal nocturnal haemoglobinuria (PNH) and paroxysmal cold haemoglobinuria ^[14]
History of gallstones (pigmented stones from chronic unconjugated hyperbilirubinaemia) ^[14]
History to elicit: family history, ethnicity, infection, drugs, transfusion history, co-existing autoimmune/lymphoproliferative diseases ^[14]

Distinguishing features:

Reticulocyte count is elevated (> 2%) — this is THE distinguishing feature from other non-megaloblastic causes where reticulocytes are low/normal
Haemolytic screen: elevated LDH, elevated unconjugated bilirubin, reduced/absent haptoglobin ^[1]^[15]
PBS: polychromasia (bluish-grey reticulocytes), spherocytes (hereditary spherocytosis, warm AIHA), schistocytes/fragmented RBCs (microangiopathic haemolysis/DIC), RBC agglutination (cold agglutinin disease), bite cells/Heinz bodies (G6PD deficiency) ^[11]^[15]
Direct antiglobulin test (DAT/Coombs) positive in immune haemolytic anaemia ^[15]

Laboratory features of haemolytic anaemia: anaemia (mildly macrocytic usually) with reticulocytosis, increase in unconjugated bilirubin, LDH, reduced serum haptoglobin, increased methaemalbumin ^[15]

Sub-classification of haemolytic anaemia as a differential ^[11]:

Category	Intravascular	Extravascular
Pathology	Haemolysis inside bloodstream → free Hb → binds haptoglobin → excess excreted in urine	Haemolysis by reticuloendothelial system (spleen, liver)
Causes	Enzyme: G6PD/PK deficiency; Fragmentation: MAHA; Complement-mediated: Cold AIHA (IgM), PNH	Membrane: HS, HE; Hb: thalassaemia, sickle cell; Warm AIHA (IgG)
Distinguishing features	Dark urine (haemoglobinuria), AKI, very low haptoglobin, urine haemosiderin	Splenomegaly, gallstones, modest LDH rise

Condition	Key Distinguishing Feature
Acute blood loss (recovery phase)	Reticulocytosis after haemorrhage; history of bleeding (GI bleed, trauma); MCV normalises as reticulocyte count falls
Multiple myeloma / paraproteinaemia	RBC rouleaux on PBS artefactually raises MCV on automated counters; elevated total protein with M-band on SPEP; bone pain, renal impairment, hypercalcaemia
Post-splenectomy	History of splenectomy; Howell-Jolly bodies on PBS (nuclear remnants not culled); target cells; mild macrocytosis
Copper deficiency	Very rare; seen after bariatric surgery or excessive zinc supplementation (zinc competes with copper absorption); causes neutropenia + macrocytic anaemia; can mimic MDS ^[13]
Congenital dyserythropoietic anaemia	Rare inherited disorder; presents in childhood/young adulthood with anaemia, jaundice, splenomegaly; BM shows multinucleated erythroblasts
Large granular lymphocyte (LGL) leukaemia	Rare; chronic neutropenia + macrocytic anaemia; PBS shows large granular lymphocytes; associated with autoimmune conditions (e.g., rheumatoid arthritis) ^[13]

While ACD is typically normocytic, it is included here because it can occasionally be mildly macrocytic (or normocytic in a patient who also has a concurrent cause of macrocytosis), and it is a common differential to consider in any anaemic patient, especially those with chronic disease.

Pathophysiology of ACD ^[17]:

Patients with ACD have adequate iron stores but iron is compartmentalized in the reticuloendothelial system ^[17]
Iron retained within RES and not made available for erythropoiesis → anaemia ^[17]
Driven by hepcidin (upregulated by IL-6 in inflammation) → hepcidin blocks ferroportin → iron trapped in macrophages

Iron profile in ACD vs IDA ^[17]:

Parameter	ACD	IDA
Serum iron	Low	Low
TIBC	Low (negative acute phase reactant)	High
Transferrin saturation	Low	Low
Serum ferritin	High (positive acute phase reactant)	Low
ESR/CRP	High	Normal

The most useful test in distinguishing IDA from ACD is TIBC ^[18] — TIBC is elevated in IDA (the body is trying to capture more iron) but low/normal in ACD (iron stores are adequate, just locked away).

Differential	MCV	Reticulocytes	PBS Clues	Key Investigation	Key Distinguishing Feature
Megaloblastic (B12/folate def)	> 100 (often > 110)	Low	Oval macrocytes, hypersegmented neutrophils	B12, folate, anti-IF/parietal cell Ab	Exclude FIRST in all macrocytic anaemias
Alcoholism	100-110	Normal	Round macrocytes, stomatocytes, target cells	GGT, alcohol history	Most common cause; normalises 2-4 months after cessation
Liver disease	100-110	Normal/mildly elevated	Round macrocytes, target cells, acanthocytes	LFT, albumin, INR	Stigmata of CLD; target cells characteristic
Hypothyroidism	100-110	Normal	Round macrocytes	TFT (TSH, fT4)	Corrects with levothyroxine; check for concurrent PA
Haemolytic anaemia	100-115	HIGH	Polychromasia, spherocytes, schistocytes	Haemolytic screen, DCT	Reticulocytosis is the hallmark
Aplastic anaemia	100-110	LOW	Normal morphology, no blasts/dysplasia	BM biopsy (hypocellular, fat-replaced)	Pancytopenia + hypocellular marrow + NO organomegaly
MDS	100-115	Low	Pseudo-Pelger-Huët, hypogranular neutrophils	BM biopsy + cytogenetics	Elderly, progressive cytopenias, NO organomegaly, may → AML
Drug-induced	100-120	Variable	Variable (may have hypersegmented neutrophils if DNA-synthesis-inhibiting drug)	Drug history, temporal relationship	Resolves after drug cessation

High Yield — Conditions That Mimic MDS

Several conditions can mimic MDS and must be actively excluded before making the diagnosis ^[13]:

Megaloblastic anaemia (B12/folate deficiency) — can cause pancytopenia and dysplastic-looking marrow; always check B12/folate
HIV infection — can cause dysplastic haematopoiesis and variable cytopenias
Copper deficiency — especially after gastric bypass surgery
Aplastic anaemia — hypocellular marrow but NO dysplasia
AML — blasts ≥ 20% rules out MDS
PMF — should have splenomegaly and JAK2 mutation

High Yield Summary — Differential Diagnosis of Non-Megaloblastic Anaemia

Always exclude megaloblastic anaemia first — check B12/folate; MCV > 120 fL is almost exclusively megaloblastic or chemotherapy-related.
The reticulocyte count bifurcates the differential: HIGH → haemolysis/blood loss recovery; LOW/NORMAL → liver disease, hypothyroidism, alcoholism, aplastic anaemia, MDS.
Most common cause overall: alcoholism (direct toxicity + membrane lipid changes).
In HK: liver disease (chronic HBV → cirrhosis) and G6PD-related haemolysis are particularly relevant.
Aplastic anaemia vs MDS: both cause pancytopenia with macrocytosis; aplastic anaemia has hypocellular marrow with morphologically NORMAL cells; MDS has dysplastic cells ± cytogenetic abnormalities.
ACD is typically normocytic but is a key differential in any anaemic patient with chronic disease; distinguished from IDA by TIBC (high in IDA, low in ACD) and ferritin (low in IDA, high in ACD).
Always take a thorough drug history — many drugs cause macrocytosis.

Active Recall – Differential Diagnosis of Non-Megaloblastic Anaemia

References

^[1] Senior notes: Maksim Medicine Notes.pdf (Haematology section, p.156-158) ^[3] Lecture slides: GC 097. Many members of the family have anaemia (File 2).pdf (p.6 – Clinical Classification of Anaemia) ^[4] Lecture slides: GC 097. Many members of the family have anaemia (PATH).pdf (p.6 – Clinical Classification of Anaemia) ^[5] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (p.7 – Aplastic anaemia section) ^[7] Senior notes: Maksim Medicine Notes.pdf (p.166-168 – Aplastic anaemia, MDS) ^[8] Senior notes: Block A - Hematology Data Interpretation.pdf (p.1 – Aplastic anaemia pathophysiology) ^[10] Senior notes: Ryan Ho Haemtology.pdf (p.29 – Pernicious anaemia, clinical features) ^[11] Senior notes: Maksim Medicine Notes.pdf (p.150-152 – Approach to anaemia, PBS morphology) ^[12] Senior notes: Block A - Pallor_ diagnosis of anaemia; nutritional anaemia; anaemia of systemic diseases.pdf (p.18 – Pernicious anaemia laboratory features) ^[13] Senior notes: Ryan Ho Haemtology.pdf (p.27, p.54, p.83 – Macrocytic anaemia approach, MDS differential) ^[14] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (p.3 – Haemolytic anaemia clinical features) ^[15] Lecture slides: Haematology Introduction to Haematological investigations (CBP, Clotting).pdf (p.32 – Haemolytic anaemia laboratory features) ^[16] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p.1468-1470 – Aplastic anaemia diagnosis) ^[17] Senior notes: Ryan Ho Chemical Path.pdf (p.54 – Anaemia of chronic disease) ^[18] Senior notes: Block A - Pallor_ diagnosis of anaemia; nutritional anaemia; anaemia of systemic diseases.pdf (p.3 – TIBC for distinguishing IDA from ACD)

1. Diagnostic Criteria

There is no single formal "diagnostic criterion set" published by a guideline body. Instead, diagnosis is established by a combination of findings:

Criterion	Requirement	Rationale
MCV > 100 fL	Must be confirmed on CBC	Defines macrocytosis
Haemoglobin below reference range	Male < 13.0 g/dL, Female < 12.0 g/dL (WHO)	Confirms anaemia is present (macrocytosis without anaemia is a separate workup)
PBS: round macrocytes with normal neutrophils	No oval macrocytes, no hypersegmented neutrophils (i.e., < 5% with 5 lobes AND < 1% with ≥ 6 lobes) ^[1]^[2]^[13]	Excludes megaloblastic morphology
Normal serum B12 and folate	Serum holotranscobalamin (active B12) > 35 pmol/L (or total B12 > 300 pg/mL); RBC folate > 150 ng/mL ^[1]^[10]	Excludes the two major megaloblastic causes
Exclude factitious macrocytosis	Rule out RBC clumping, cold agglutinins, hyperglycaemia-induced osmotic swelling, prolonged EDTA storage ^[13]	Automated analysers can artefactually raise MCV

GC High Yield – Excluding Megaloblastic Anaemia

From GC 076 lecture slides, investigations for suspected pernicious anaemia (the main megaloblastic cause to exclude) include: serum Vitamin B12 level, serum holotranscobalamin, serum and red cell folate level, anti-parietal cell antibody (sensitive but less specific), anti-intrinsic factor antibody (specific but less sensitive), upper endoscopy (atrophic gastritis and carcinoma of stomach), Schilling test (historical interests, obsolete in HK), bone marrow examination (not routinely needed, except when laboratory findings incompatible with PA) ^[19]^[12].

1.2 Formal Diagnostic Criteria for Specific Underlying Causes

This is the most formally codified set of diagnostic criteria among the non-megaloblastic causes:

From GC 047 lecture slides — Aplastic anaemia investigations: Blood count (pancytopenia, macrocytic anaemia, low reticulocyte count), blood film, autoimmune markers, Vit B12 and folate levels, bone marrow (trephine biopsy required for assessment of cellularity), specialized tests (flow cytometry for CD55/CD59 deficient RBC to rule out PNH; chromosome breakage with diepoxybutane to screen for Fanconi anaemia) ^[22].

Severity	Criteria
Very severe AA (vSAA)	Meets severe AA criteria AND ANC < 0.2 × 10⁹/L ^[7]^[20]^[21]
Severe AA (SAA)	BM cellularity < 25% (or 25-50% if < 30% of residual cells are haematopoietic) AND ≥ 2 of following: (1) ANC < 0.5 × 10⁹/L, (2) platelet < 20 × 10⁹/L, (3) reticulocyte < 20 × 10⁹/L ^[7]^[20]^[21]
Non-severe AA (nSAA)	BM cellularity < 25% (or 25-50% if < 30% of residual cells are haematopoietic) AND peripheral blood cytopenias not fulfilling criteria for SAA ^[7]^[20]^[21]

Why these specific thresholds?

ANC < 0.5: Below this level, risk of serious bacterial/fungal infections rises steeply. Below 0.2, risk is extreme.
Platelets < 20: Below this, spontaneous mucocutaneous bleeding risk is significant.
Reticulocyte < 20: Confirms marrow failure (the marrow cannot mount a compensatory response despite anaemia and high EPO levels).

Essential diagnostic requirements for AA ^[16]^[20]^[21]:

BM biopsy is REQUIRED for diagnosis — aspiration alone is insufficient because you need to assess cellularity (how much of the marrow space is occupied by haematopoietic tissue vs fat)
Hypocellular marrow with prominent fat cells and marrow stroma
Residual haematopoietic cells are morphologically NORMAL and haematopoiesis is NOT megaloblastic
NO evidence of malignant infiltration or fibrosis
Cytogenetics (karyotyping/FISH) must be performed to exclude hypocellular MDS ^[16]
Flow cytometry for CD55/CD59 to exclude PNH ^[16]^[22]

3. Investigation Modalities — Detailed Interpretation

The CBC is the first-line investigation for any anaemia. For non-megaloblastic macrocytic anaemia, focus on:

Parameter	Expected Finding	Interpretation & Why
Haemoglobin	Low (below reference)	Confirms anaemia; severity guides urgency
MCV	> 100 fL	Defines macrocytosis. MCV > 110-115 fL almost exclusively megaloblastic ^[13]; non-megaloblastic causes rarely push MCV above 110-115
MCH	Usually proportionally raised	MCH rises because cells are larger and carry more Hb per cell (though Hb concentration may be normal → MCHC often normal)
MCHC	Normal	Unlike spherocytosis (where MCHC is elevated because the cell is smaller but same Hb content)
RDW	Variable	Elevated in mixed/dimorphic anaemia (e.g., concurrent iron deficiency + macrocytic cause); normal in pure non-megaloblastic macrocytosis
WBC	Low in aplastic anaemia/MDS; normal in liver disease/hypothyroidism	Pancytopenia points towards marrow failure
Platelets	Low in aplastic anaemia/MDS; normal/high in liver disease (early), low (late → hypersplenism)	Thrombocytopenia + macrocytic anaemia = high suspicion for marrow pathology
Reticulocyte count	Critical branching point	High (> 2%) → haemolysis or blood loss recovery; Low/normal → marrow failure or non-marrow cause ^[1]^[13]

The PBS is the single most important investigation for classifying macrocytic anaemia. It provides morphological information that automated analysers cannot.

PBS Finding	Points Towards	Why
Round macrocytes	Non-megaloblastic (liver disease, alcohol, hypothyroidism) ^[1]	Excess membrane lipid → uniform enlargement without nuclear maturation defect
Oval macrocytes	Megaloblastic (B12/folate deficiency) ^[1]^[2]	Nuclear-cytoplasmic asynchrony → abnormal cell shape during maturation
Hypersegmented neutrophils (≥ 5% with 5 lobes or ≥ 1% with ≥ 6 lobes) ^[2]^[10]	Megaloblastic	Impaired DNA synthesis in the myeloid lineage → continued nuclear division without cytoplasmic division → excess lobes
Polychromasia	Reticulocytosis → haemolytic anaemia or blood loss recovery ^[14]^[15]	Reticulocytes stain blueish-grey on Wright stain due to residual RNA
Target cells	Liver disease, thalassaemia, post-splenectomy ^[13]	Excess membrane lipid or reduced cell contents → central pallor surrounded by ring of Hb
Spherocytes	Hereditary spherocytosis, warm AIHA ^[15]	Loss of membrane surface area → cell becomes sphere-shaped
Schistocytes (fragmented RBCs)	MAHA (TTP/HUS, DIC), mechanical valve ^[11]^[15]	Physical shearing of RBCs by fibrin strands or prosthetic surfaces
RBC agglutination	Cold agglutinin disease ^[15]	IgM autoantibodies cause RBC clumping at low temperatures
Pseudo-Pelger-Huët anomaly	MDS ^[13]	Dysplastic neutrophils with bilobed "pince-nez" nuclei
Tear-drop cells (dacrocytes)	Myelofibrosis, marrow infiltration	RBCs are distorted as they squeeze through fibrotic marrow sinusoids
Howell-Jolly bodies	Post-splenectomy, MDS, megaloblastic anaemia ^[11]	Nuclear remnants not cleared because spleen is absent or dysfunctional
Stomatocytes	Alcoholism, liver disease	Altered membrane lipid composition → mouth-shaped central pallor
Acanthocytes (spur cells)	Severe liver disease (spur cell anaemia), abetalipoproteinaemia	Irregular cholesterol deposition in membrane

These are mandatory to exclude megaloblastic anaemia before diagnosing a non-megaloblastic cause.

Test	Normal Range	Interpretation
Serum B12 (total)	> 300 pg/mL normal; 200-300 borderline; < 200 deficient ^[10]	Measures both active (transcobalamin-bound) and inactive (haptocorrin-bound) fractions
Serum holotranscobalamin (active B12)	> 35 pmol/L	The active fraction (10-30% of total B12) ^[1]; more accurate than total B12; this is what we use nowadays ^[12]
RBC folate	> 150 ng/mL indicates adequate stores ^[10]	More reliable than serum folate (reflects intracellular stores over preceding 3 months)
Serum folate	Reference range varies	May be influenced by recent dietary intake, alcohol, drugs ^[10]; less reliable

Why check both B12 AND folate? Because B12 deficiency can falsely elevate serum folate levels (B12 normally "traps" folate into cells — the methyl-folate trap; without B12, folate accumulates extracellularly) ^[1]. Checking only serum folate in the presence of B12 deficiency may give a false sense of reassurance.

If B12/folate levels are equivocal ^[10]:

Methylmalonic acid (MMA) and homocysteine levels:
- B12 deficiency: ↑MMA, ↑homocysteine
- Folate deficiency: normal MMA, ↑homocysteine
- Both normal: no B12/folate deficiency ^[1]

Finding	Interpretation
Elevated (> 2% or absolute count > 100 × 10⁹/L)	Appropriate marrow response to peripheral RBC destruction/loss → haemolysis or recent blood loss
Low or inappropriately normal	Marrow failure (aplastic anaemia, MDS) or non-marrow cause (liver disease, hypothyroidism, alcoholism)

Why "inappropriately normal"? If a patient is anaemic, EPO should be high → marrow should be producing reticulocytes briskly. A "normal" reticulocyte count in the face of significant anaemia is actually inappropriately low and suggests the marrow is failing.

Ordered when reticulocytes are elevated to confirm haemolysis:

Test	Expected in Haemolysis	Mechanism
LDH	Elevated	Released from lysed RBCs (LDH-1 and LDH-2 isoforms predominate)
Unconjugated (indirect) bilirubin	Elevated	Hb → haem → biliverdin → unconjugated bilirubin; overwhelms hepatic conjugation capacity
Haptoglobin	Reduced or absent ^[15]	Haptoglobin binds free Hb released from lysed RBCs → cleared by RES → consumed
Methemalbumin	Increased ^[15]	Once haptoglobin is saturated, haem binds albumin → methemalbumin
Urine haemoglobin/haemosiderin	Positive in intravascular haemolysis	Free Hb filtered by glomerulus; haemosiderin accumulates in renal tubular cells and is shed into urine
Direct antiglobulin test (DAT/Coombs)	Positive in immune haemolytic anaemia ^[15]	Detects IgG or complement (C3d) bound to RBC surface

According to the Haematology Introduction lecture slides: haemolytic anaemia laboratory features include anaemia (mildly macrocytic usually) with reticulocytosis, increase in unconjugated bilirubin, LDH, reduced serum haptoglobin, increased methemalbumin. Blood film shows polychromasia, spherocytes (hereditary spherocytosis, immune haemolytic anaemia), RBC fragmentation (microangiopathic haemolysis), RBC agglutination (cold agglutinin disease). Direct antiglobulin test is positive in immune haemolytic anaemia. ^[15]

After confirming haemolysis, the next step depends on DAT result ^[14]:

DAT positive → immune-mediated → classify as warm (IgG) vs cold (IgM/complement), investigate underlying cause (autoimmune, lymphoproliferative, drug-induced)
DAT negative → intrinsic RBC defect → further workup:
- G6PD assay
- Haemoglobin electrophoresis/HPLC
- Osmotic fragility test (hereditary spherocytosis)
- Flow cytometry for GPI-anchored proteins (PNH)

After confirming a patient has haemolysis, the next step to determine whether the patient is undergoing autoimmune-mediated destruction is the direct antiglobulin test. It will be positive in immune haemolytic anaemias. However, some proportion of the healthy population will have positive DAT but no haemolysis → pre-test probability must be established first ^[14].

Parameter	Findings in Liver Disease-Related Macrocytosis
Bilirubin	Elevated (mixed or conjugated in liver disease; unconjugated if concurrent haemolysis)
ALT/AST	Elevated (hepatocellular damage)
AST:ALT ratio	> 2 suggests alcoholic liver disease
ALP/GGT	Elevated GGT is the most sensitive marker of alcohol use
Albumin	Low (reduced synthetic function in cirrhosis)
INR/PT	Prolonged (impaired clotting factor synthesis)

Parameter	Findings in Hypothyroidism
TSH	Elevated (primary hypothyroidism)
Free T4	Low

Simple and definitive. If TSH is raised and fT4 is low, hypothyroidism explains the macrocytosis. Treat with levothyroxine and monitor Hb/MCV response.

While primarily used for microcytic anaemia, iron studies are important in the non-megaloblastic workup to:

Exclude concurrent iron deficiency (creating a dimorphic picture where the MCV may be "normal" — averaged between micro and macro populations)
Assess for iron overload in aplastic anaemia/MDS (from repeated transfusions)

Parameter	IDA	ACD	Iron Overload
Serum iron	↓	↓	↑
TIBC	↑	↓	↓
Transferrin saturation	↓ ( < 16%)	↓	↑ (> 45%)
Serum ferritin	↓ (diagnostic of IDA) ^[23]^[24]	↑ (acute phase reactant) ^[17]	↑ (> 200 M, > 150 F)

Serum ferritin: most sensitive and specific marker for iron deficiency. Low serum ferritin is diagnostic of iron deficiency. Clinical decision cutoffs: Adults < 34 pmol/L (15 μg/L); Elderly hospitalized < 100 pmol/L (45 μg/L); Community-based elderly < 49 pmol/L (22 μg/L) ^[23].

Serum Fe CANNOT be used alone. Transferrin Fe saturation CANNOT be used alone ^[23]. Always interpret the full iron profile together.

When to order: Unexplained pancytopenia, suspected aplastic anaemia or MDS, failure to respond to treatment, uncertain diagnosis after initial workup ^[12]^[13]^[16].

Technique	What It Provides
Aspirate	Cytology (morphology of individual cells), flow cytometry, cytogenetics, molecular genetics ^[25]
Trephine biopsy	Histological architecture — marrow cellularity, pattern of involvement, fibrosis, bone structure ^[25]; also immunohistochemistry

BM aspirate and trephine biopsy can be performed at different sites 1-2cm apart. Absolute contraindication: severe bleeding disorders (DIC, severe haemophilia) — but thrombocytopenia of any severity is NOT a contraindication; just transfuse to > 20 × 10⁹/L beforehand ^[25].

Key BM findings by diagnosis:

Diagnosis	BM Aspirate	BM Trephine
Aplastic anaemia	Profoundly hypocellular, decrease in all elements ^[20]^[21]; morphologically normal residual cells, NOT megaloblastic ^[16]^[20]	> 90% fat replacement; NO malignant infiltration or fibrosis ^[7]^[16]^[20]
MDS	Dysplastic morphology in ≥ 1 lineage; ring sideroblasts on Prussian blue stain; blast count < 20% ^[7]	Variable cellularity (often hyper- or normocellular); may show mild fibrosis
Myelofibrosis	Dry tap (cannot aspirate due to fibrosis)	Dense reticulin on silver stain ^[26]; tear-drop cells on PBS
Marrow infiltration (leukaemia, lymphoma, metastasis)	Abnormal cells (blasts, lymphoma cells, metastatic carcinoma)	Architectural disruption by malignant cells

3.10 Specialised Investigations

Test	When to Order	What It Shows
GGT	Suspected alcohol use	Most sensitive marker of alcohol use; rises even with moderate intake
G6PD assay	Suspected G6PD deficiency (especially HK males with episodic haemolysis)	Enzyme activity reduced; may be falsely normal during acute haemolysis (reticulocytes have higher G6PD activity) — recheck 2-3 months later
Hb electrophoresis/HPLC	Suspected haemoglobinopathy	Identifies abnormal Hb variants (HbS, HbC, HbH, unstable Hb)
Osmotic fragility test	Suspected hereditary spherocytosis	Spherocytes lyse at higher saline concentrations than normal biconcave RBCs
Anti-parietal cell Ab, anti-IF Ab	Suspected pernicious anaemia (even if presenting as mixed picture)	Anti-parietal cell Ab: sensitive but less specific; Anti-IF Ab: specific but less sensitive ^[12]^[19]
Serum TSH, fT4	All macrocytic anaemia patients	Exclude hypothyroidism — simple and cheap
Hepatitis serology	Suspected liver disease or pre-aplastic anaemia hepatitis	HBsAg, anti-HCV; also check non-A,B,C hepatitis in aplastic anaemia workup
Autoimmune markers (ANA, anti-dsDNA)	Suspected autoimmune aetiology	May identify underlying SLE or autoimmune condition driving cytopenias ^[16]

Step	Action	Key Finding → Next Step
1	CBC with indices + reticulocyte count	MCV > 100, Hb low → macrocytic anaemia confirmed
2	PBS	Round macrocytes + normal neutrophils → non-megaloblastic
3	Serum B12 (holotranscobalamin) + RBC folate	Normal → confirms non-megaloblastic
4	Reticulocyte count (already from Step 1)	High → haemolytic screen (Step 5a); Low/normal → Step 5b
5a	Haemolytic screen: LDH, unconjugated bilirubin, haptoglobin, DAT	Confirms haemolysis; DAT +ve → immune; DAT −ve → intrinsic defect workup
5b	LFT, TFT, GGT, alcohol/drug history	Identifies liver disease, hypothyroidism, alcoholism, drug cause
6	If all above normal → BM biopsy with cytogenetics	Aplastic anaemia vs MDS vs marrow infiltration
7	Specialised tests based on BM findings	PNH screen (flow cytometry), Fanconi screen (DEB test), MDS cytogenetics

High Yield — Investigation Priority in Non-Megaloblastic Macrocytic Anaemia

The non-megaloblastic macrocytic anaemia investigation panel from Maksim Medicine Notes: haemolytic screen (LDH, haptoglobin, bilirubin, reticulocyte), LFT, TFT ^[1]. This is the minimum "screening battery" after confirming B12/folate are normal and PBS shows round macrocytes.

High Yield Summary — Diagnostics

Non-megaloblastic macrocytic anaemia is diagnosed by: MCV > 100, round macrocytes + normal neutrophils on PBS, normal B12/folate.
Reticulocyte count is the key branching investigation: elevated → haemolysis workup; low/normal → LFT, TFT, alcohol history → if all normal, BM biopsy.
Aplastic anaemia requires BM trephine biopsy for diagnosis: hypocellular marrow (< 25% cellularity), fat replacement, morphologically normal residual cells, no fibrosis/malignancy. Always exclude PNH (flow cytometry for CD55/CD59) and Fanconi anaemia (DEB test in children).
MDS requires BM biopsy + cytogenetics: dysplastic morphology, blast count < 20%, ring sideroblasts, characteristic cytogenetic abnormalities. Always check B12/folate first.
Ferritin is the most sensitive and specific marker for iron deficiency, but is a positive acute phase reactant → can be falsely normal/elevated in inflammation. TIBC is the most useful single test to distinguish IDA from ACD.
MCV > 110-115 fL is almost exclusively megaloblastic — if you see this, think B12 deficiency or chemotherapy before non-megaloblastic causes.

Active Recall – Diagnostics of Non-Megaloblastic Anaemia

2. General Supportive Management (Applies to All Causes)

Before diving into cause-specific treatments, every patient with non-megaloblastic macrocytic anaemia needs these general measures addressed:

When to transfuse?

Indication	Threshold	Rationale
Angina, heart failure, cerebral hypoxia ^[24]^[27]	Transfuse regardless of Hb	Tissue ischaemia demands immediate oxygen-carrying capacity restoration
Symptomatic severe anaemia	Hb < 7 g/dL ^[24]^[27]	Below this threshold, compensatory mechanisms (↑CO, ↑2,3-BPG) are inadequate
Chronic transfusion-dependent patients (aplastic anaemia, MDS)	Keep Hb above a functional threshold (typically > 7-8 g/dL)	Maintain quality of life and functional capacity

Why not transfuse liberally?

Each unit of packed RBCs contains ~250 mg of elemental iron ^[1] → repeated transfusions cause iron overload (haemochromatosis), damaging liver, heart, and endocrine organs
Transfusion reactions (febrile, allergic, haemolytic)
Alloimmunisation → makes future transfusions and HSCT more difficult
In aplastic anaemia patients being considered for HSCT, minimise transfusions to reduce alloimmunisation risk

Indicated in transfusion-dependent patients (aplastic anaemia, MDS, thalassaemia) to prevent transfusional iron overload.

When to start chelation? When ferritin > 1000 μg/L or positive MRI findings of iron deposition in liver/heart ^[1].

Agent	Route	Key Features	Side Effects
Deferoxamine (Desferal)	SC infusion 3-5×/week	Gold standard; long track record	Ototoxicity, retinal changes, ARDS; compliance issues due to subcutaneous infusion ^[1]
Deferasirox (Exjade/Jadenu)	PO once daily	Convenient oral; widely used	GI upset, LFT/RFT derangements, hypotension, hypersensitivity ^[1]
Deferiprone (Ferriprox)	PO	Less effective than above; sometimes used in combination	Agranulocytosis (monitor FBC regularly) ^[1]

Why does iron overload matter?

Excess iron saturates transferrin → non-transferrin-bound iron (NTBI) appears, bound loosely to albumin/citrate → NTBI catalyses the Haber-Weiss reaction (iron + H₂O₂ → reactive oxygen species) → oxidative tissue damage ^[1]
Target organs: liver (cirrhosis), heart (dilated cardiomyopathy → heart failure), endocrine (DM, hypogonadism, hypothyroidism), skin (hyperpigmentation → "bronze diabetes")

3. Cause-Specific Management

Management is straightforward: alcohol cessation.

Intervention	Details	Mechanism/Rationale
Alcohol cessation	The definitive treatment	Removes the direct toxic effect on erythroid precursors and normalises hepatic lipid metabolism → membrane lipid abnormality resolves
Expect MCV normalisation in 2-4 months	Matches RBC lifespan (~120 days)	Existing macrocytic RBCs must be replaced by new, normal-sized cells
Nutritional supplementation	Thiamine (B1), folate, multivitamins	Alcoholics frequently have multiple nutritional deficiencies; thiamine to prevent/treat Wernicke's encephalopathy
Screen for concurrent deficiencies	Check B12, folate, iron	Alcoholism commonly coexists with folate deficiency (poor diet + impaired absorption) and iron deficiency (GI bleeding from varices/gastritis)
Treat underlying liver disease if present	Manage cirrhosis, portal hypertension	The macrocytosis from liver disease has a separate mechanism from the direct alcohol effect

The macrocytosis improves when the liver disease is controlled, though in advanced cirrhosis it may persist.

Intervention	Details
Treat underlying liver disease	Antivirals for HBV (entecavir, tenofovir) / HCV (DAAs); abstinence for alcoholic liver disease; weight loss for NAFLD/MASLD
Manage portal hypertension	Non-selective beta-blockers, endoscopic variceal ligation for varices
Address hypersplenism	If splenomegaly causes significant cytopenias → consider TIPS or splenectomy in selected cases
Liver transplantation	For end-stage liver disease (Child-Pugh C, MELD score criteria) → definitive cure; anaemia resolves post-transplant
Concurrent iron deficiency	Common in cirrhotics (variceal bleeding, gastric erosions) → iron supplementation after confirming IDA

Intervention	Details
Levothyroxine replacement	Start low (25-50 μg/day) and titrate to normalise TSH (especially in elderly/cardiac patients — risk of precipitating angina/arrhythmia with rapid correction)
Monitor Hb/MCV	Should normalise within 3-6 months of achieving euthyroid state
Screen for concurrent pernicious anaemia	Autoimmune thyroiditis and pernicious anaemia frequently coexist (autoimmune clustering) → check B12, anti-IF antibody

3.4 Haemolytic Anaemia

Management depends on the specific type of haemolytic anaemia. The general principles and cause-specific treatments:

Type	Key Management	Why
Warm AIHA (IgG)	Steroids (prednisolone 1 mg/kg/day) → first line; rituximab (anti-CD20) or splenectomy for refractory cases ^[11]	IgG-coated RBCs are destroyed by splenic macrophages → steroids suppress autoimmune response; splenectomy removes the primary site of extravascular destruction
Cold agglutinin disease (IgM)	Avoid cold exposure; rituximab ± bendamustine; steroids less effective; splenectomy NOT helpful	IgM activates complement on RBCs → destruction mainly intravascular and hepatic (not splenic) → splenectomy ineffective
G6PD deficiency	Avoid triggers (fava beans, infections, oxidant drugs — primaquine, dapsone, sulfonamides); supportive care during crises	No chronic treatment needed; enzyme deficiency is lifelong but haemolysis is episodic; between crises patients are well
Hereditary spherocytosis	Folic acid supplementation; splenectomy for severe haemolysis ^[28]^[29]	Spherocytes are selectively trapped and destroyed in splenic sinusoids → splenectomy dramatically reduces haemolysis
PNH	Eculizumab or ravulizumab (anti-C5 monoclonal antibody) → blocks terminal complement activation; anticoagulation for thrombosis	PNH RBCs lack CD55/CD59 → uncontrolled complement activation on surface → intravascular haemolysis; blocking C5 prevents MAC formation

Splenectomy indications in haemolysis: refractory ITP or AIHA (less common); decrease transfusion requirement in thalassaemia major; symptomatic relief in massive splenomegaly ^[31].

Complications of Splenectomy – Must Know

Post-splenectomy patients are at risk of life-threatening infection from encapsulated bacteria (overwhelming post-splenectomy infection — OPSI) ^[31]. Preventive measures:

Vaccinations: pneumococcal, meningococcal, Haemophilus influenzae type b — give ≥ 2 weeks before elective splenectomy
Prophylactic antibiotics: lifelong penicillin V (or amoxicillin) for at-risk patients, at minimum for 2 years and ideally lifelong for children
Patient education: seek medical attention immediately for any febrile illness
Timing: Usually deferred until > 6-7 years old to reduce risk of sepsis ^[28]^[29]

Post-splenectomy blood findings that are expected (not alarming) ^[31]:

Spurious leukocytosis, increased platelet count
Howell-Jolly bodies on PBS (nuclear remnants no longer culled by the spleen)

3.5 Aplastic Anaemia

This is the most complex management pathway among the non-megaloblastic causes, and highly examinable.

GC High Yield – Aplastic Anaemia Treatment

From GC 047 and senior notes: Treatment of severe aplastic anaemia includes (1) first line for young patients with matched sibling donors: allogeneic HSCT; (2) anti-thymocyte globulin + cyclosporine A; (3) eltrombopag (high dose) + ATG + CsA; (4) supportive treatment: blood products, iron chelation ^[5]^[7]^[20].

Treatment	Indication	Mechanism / Rationale	Key Considerations
Allogeneic HSCT	First line for young patients (< 40 yo) with HLA-matched sibling donor ^[5]^[7]^[20]	Replaces the destroyed haematopoietic stem cells with healthy donor stem cells → the only potentially curative treatment	Conditioning regimen (usually reduced intensity in AA); graft-vs-host disease risk; transplant-related mortality ~10-15% with matched sibling
Anti-thymocyte globulin (ATG)	Part of first-line immunosuppression for patients unsuitable for HSCT ^[5]^[7]^[20]	ATG (derived from horse or rabbit serum) depletes the autoreactive T cells that are destroying HSCs → allows marrow recovery	Give horse ATG (hATG) preferentially — shown superior to rabbit ATG in AA; requires hospitalisation for infusion; risk of serum sickness, anaphylaxis
Cyclosporine A (CsA)	Combined with ATG as part of immunosuppressive regimen ^[5]^[7]^[20]	Calcineurin inhibitor → suppresses T cell activation → reduces ongoing immune-mediated HSC destruction	Monitor trough levels; side effects: nephrotoxicity, hypertension, gingival hyperplasia, tremor; taper slowly (rapid discontinuation → relapse)
Eltrombopag	Added to ATG + CsA as triple therapy ^[5]^[20]	Thrombopoietin receptor agonist → stimulates HSC proliferation (not just megakaryocytes) → enhances marrow recovery	High-dose eltrombopag (150 mg/day) added to ATG + CsA has shown improved response rates vs ATG + CsA alone; monitor LFTs
Supportive care ^[7]	All patients	Address the consequences of pancytopenia	See transfusion, chelation, infection management above
Androgens (e.g., danazol, oxymetholone)	Consider in selected cases ^[7]	Stimulate erythropoiesis by increasing EPO production and direct marrow stimulation; also upregulate telomerase activity (relevant in telomere biology disorders like dyskeratosis congenita)	Side effects: virilisation, hepatotoxicity; mainly used when IST has failed or as adjunct
Discontinue offending drugs ^[7]	If drug-related AA suspected	Remove the trigger for marrow destruction	Chloramphenicol, NSAIDs, anticonvulsants, benzene exposure

Response assessment:

Response to immunosuppression typically takes 3-6 months → do not declare failure too early
Screen for developing clonal disorders: MDS, PNH, AML over time ^[7] — aplastic anaemia can evolve into these

Prognosis ^[20]:

70% 1-year mortality if untreated
80-90% 5-year survival if treated (HSCT or IST)

3.6 Myelodysplastic Syndrome (MDS)

MDS management is risk-stratified — not all MDS patients require treatment. This is a critical concept.

Key Principle: NOT ALL MDS Require Treatment

No current treatment is curative for MDS (except allogeneic HSCT in selected patients). There is no evidence that treatment of asymptomatic patients prolongs survival. Main goal: control symptoms and improve quality of life. ^[32]

Treatment	Indication	Mechanism	Key Points
Erythropoiesis-stimulating agents (ESA, e.g., epoetin alfa, darbepoetin)	Low-risk MDS with isolated anaemia and EPO ≤ 500 mU/mL ^[32]	Stimulates erythroid progenitors in the bone marrow to increase RBC production	Response rate ~40-60%; duration of response variable; check endogenous EPO level before starting — high endogenous EPO ( > 500) predicts poor response
Luspatercept (Reblozyl)	MDS with ring sideroblasts (MDS-RS) ^[9]^[32]	Activin receptor fusion protein that acts as a ligand trap → neutralises TGF-β superfamily ligands → releases the brake on late-stage erythroid maturation by blocking overactive SMAD2/3 signalling ^[9]	SC injection every 3 weeks; reduces transfusion dependence; approved specifically for MDS-RS ± SF3B1 mutation
Lenalidomide	MDS with isolated del(5q) ^[7]^[32]	Immunomodulatory drug; selectively cytotoxic to del(5q) clone (degrades casein kinase 1α, which is haploinsufficient in del(5q) cells)	Can achieve transfusion independence in ~67%; risk of neutropenia and thrombocytopenia; requires VTE prophylaxis
Hypomethylating agents (HMA): azacitidine, decitabine	Low-risk MDS with bi/pancytopenia without actionable mutations; intermediate-risk MDS ^[32]	Decrease methylation of CpG islands → decrease gene silencing → re-expression of tumour suppressor genes ^[32]	Not curative but shown to increase survival ^[32]; treatment must be continued indefinitely (responses lost on cessation); give SC or IV every 4 weeks
Immunosuppressive therapy (ATG + CsA)	Selected low-risk MDS patients (especially younger patients with hypocellular marrow, resembling aplastic anaemia) ^[32]	Suppresses autoreactive T cells (similar rationale to AA)	Best responses in hypocellular MDS with HLA-DR15 positivity
TPO receptor agonists (e.g., romiplostim, eltrombopag)	Isolated thrombocytopenia refractory to transfusion ^[32]	Stimulates megakaryopoiesis	Caution: concerns for increased transformation to AML as it may stimulate growth of leukaemic blasts ^[32]
Allogeneic HSCT	High-risk MDS in patients fit for transplant ^[7]^[32]	Only potentially curative treatment; replaces the dysplastic clone with healthy donor haematopoiesis	Transplant-related mortality significant; usually for patients < 70 years with acceptable performance status and comorbidities
Intensive induction chemotherapy	High-risk MDS unfit for HSCT or as bridge to HSCT	Cytoreductive — aims to reduce blast burden	Similar regimens to AML induction (e.g., "7+3" cytarabine + daunorubicin); often poor outcomes in MDS compared to de novo AML

While renal anaemia is typically normochromic normocytic ^[33], it is included here because CKD patients may have concurrent macrocytic causes (drugs, folate deficiency, etc.), and the treatment of renal anaemia is highly examinable.

Renal anaemia guideline (UK): Hb target between 10 to 11 g/dL, but not greater than 12 g/dL. Iron saturation > 20%. Serum ferritin at least 100 in pre-dialysis patients, 200 in hemodialysis patients ^[34].

Treatment	Details
ESA (epoetin alfa/beta, darbepoetin)	Replaces deficient EPO; target Hb 10-11 g/dL; do NOT overcorrect (risk of hypertension, stroke, thrombosis)
Iron supplementation	Often IV iron (ferric carboxymaltose, iron sucrose) in dialysis patients — oral iron poorly absorbed in CKD
HIF-PHI (roxadustat, daprodustat)	Newer oral agents; inhibit prolyl hydroxylase → stabilise HIF → increase endogenous EPO and improve iron utilisation

Approach	Details
Discontinue or substitute	If the offending drug can be safely stopped or switched to a non-macrocytosis-causing alternative
Monitor	If the drug is essential (e.g., azathioprine for transplant immunosuppression, hydroxyurea for MPN) → macrocytosis is an expected pharmacodynamic effect and does not necessarily warrant discontinuation
Dose adjustment	Sometimes reducing the dose can mitigate the macrocytosis while maintaining therapeutic efficacy

Cause	Monitoring Plan
Alcoholism	MCV every 1-3 months after cessation; GGT as compliance marker; screen for liver disease
Liver disease	Regular LFT, albumin, INR; hepatocellular carcinoma surveillance (USS + AFP q6 months for cirrhotics); Hb monitoring
Hypothyroidism	TSH every 6-8 weeks until stable on levothyroxine, then annually; Hb/MCV should normalise within 3-6 months
Haemolytic anaemia	Hb, reticulocyte count, LDH, haptoglobin regularly; bilirubin; USS for gallstones; folate levels
Aplastic anaemia	CBC/differential regularly; screen for developing clonal disorders (MDS, PNH, AML) over time ^[7]; ferritin for iron overload in transfusion-dependent patients; organ iron assessment by MRI
MDS	Regular CBC/differential and PBS ^[32]; blast count monitoring; cytogenetics at disease progression; watch for transformation to AML

Complications management will be covered in full detail in the next section, but brief mention of key complication-specific treatments:

Complication	Treatment
Iron overload (transfusion-related)	Iron chelation (deferoxamine, deferasirox, deferiprone); venesection if tolerated ^[1]
Pigment gallstones	Cholecystectomy if symptomatic ^[11]
Overwhelming post-splenectomy infection (OPSI)	Prevention: vaccinations + prophylactic antibiotics; Treatment: urgent IV antibiotics covering encapsulated organisms
Transformation to AML (from MDS)	Intensive chemotherapy ± allogeneic HSCT
High-output cardiac failure (severe chronic anaemia)	Transfusion (cautiously, with diuretics to avoid fluid overload), treat underlying cause

High Yield Summary — Management

General principle: Non-megaloblastic macrocytic anaemia management = treat the underlying cause + supportive care.
Alcoholism: cessation → MCV normalises in 2-4 months.
Liver disease: treat the liver disease; macrocytosis improves with disease control.
Hypothyroidism: levothyroxine; Hb/MCV normalises in 3-6 months.
Haemolytic anaemia: folate supplementation for all; cause-specific (steroids for AIHA, avoid triggers for G6PD, splenectomy for HS, eculizumab for PNH).
Aplastic anaemia: First line for young patients with HLA-matched sibling = allogeneic HSCT. Otherwise: ATG + CsA ± eltrombopag (triple immunosuppression). Supportive: transfusion, chelation, G-CSF, antibiotics. Screen for PNH/MDS/AML.
MDS: Risk-stratified. Low risk: monitor ± ESA ± targeted therapy (lenalidomide for del(5q), luspatercept for MDS-RS). High risk: allogeneic HSCT or intensive chemo. HMA (azacitidine) for intermediate risk.
Iron chelation: Start when ferritin > 1000 μg/L; options: deferoxamine (SC), deferasirox (PO), deferiprone (PO).
Post-splenectomy: vaccinate against encapsulated organisms, lifelong prophylactic penicillin, patient education.

Active Recall – Management of Non-Megaloblastic Anaemia

1. Complications of the Anaemia Itself

These are common to all anaemias when they become sufficiently severe or chronic. The pathophysiology always traces back to reduced oxygen-carrying capacity → tissue hypoxia → compensatory mechanisms that eventually become maladaptive.

Complication	Pathophysiological Mechanism	Clinical Presentation
High-output cardiac failure	Chronic anaemia → ↓O₂ delivery → compensatory ↑cardiac output (↑HR + ↑SV) + peripheral vasodilation → over time, the heart cannot sustain this increased workload → ventricular dilation and failure	Dyspnoea, peripheral oedema, raised JVP, bibasal crepitations, hepatomegaly; noncardiac cause of raised BNP ^[35]
Cardiac ischaemia ^[10]^[36]	Reduced O₂ content in blood → myocardial O₂ supply-demand mismatch, especially in patients with pre-existing coronary artery disease; even moderate anaemia can precipitate angina or NSTEMI	Chest pain, ECG changes (ST depression, T-wave inversion); may present as MINOCA in younger patients without overt CAD
Arrhythmias	Chronic myocardial hypoxia + sympathetic activation (compensatory tachycardia) → increased myocardial excitability	Palpitations, AF, ventricular ectopics

Complications of anaemia include: cardiac ischaemia, increased thrombocytopenic bleeding, and increased mortality ^[10]^[36].

Why does high-output failure occur? Let's trace it from first principles:

Anaemia → ↓Hb → ↓O₂ content per unit of blood → tissues sense hypoxia
Compensatory mechanisms: ↑2,3-BPG (shifts O₂-dissociation curve right → easier unloading), ↑cardiac output (↑HR via sympathetic drive, ↑SV via Frank-Starling), peripheral vasodilation (↓afterload)
These mechanisms maintain tissue oxygenation in mild-moderate anaemia
But sustained ↑CO → eccentric ventricular hypertrophy → eventually systolic dysfunction → decompensated heart failure

Complication	Mechanism
Cognitive impairment, confusion	Cerebral hypoxia from reduced O₂ delivery
Syncope	Severe anaemia → cerebral hypoperfusion, especially postural
Exacerbation of pre-existing neurodegenerative conditions	Reduced cerebral O₂ reserve → accelerates functional decline

2. Complications Specific to Underlying Causes

Relevant to haemolytic anaemia as a non-megaloblastic cause of macrocytosis.

Complication	Pathophysiology	Clinical Features & Management
Pigment (bilirubin) gallstones ^[14]^[11]	Chronic unconjugated hyperbilirubinaemia → excess bilirubin excreted in bile → calcium bilirubinate precipitation → black pigment stones	Biliary colic, cholecystitis, cholangitis; cholecystectomy if symptomatic ^[11]
Aplastic crisis	Parvovirus B19 infection → tropism for erythroid progenitors (binds P antigen/globoside) → transient cessation of erythropoiesis → in patients dependent on high erythroid turnover (haemolysis), even brief marrow suppression causes precipitous Hb drop	Sudden severe anaemia; reticulocyte count drops to near zero; self-limiting in 1-2 weeks in immunocompetent; supportive transfusion; IVIg in immunocompromised
Folate deficiency	Chronic haemolysis → ↑RBC turnover → ↑folate demand → depletion of body stores (only ~3 months' reserve) → megaloblastic anaemia superimposed on haemolytic anaemia	Worsening anaemia with new appearance of oval macrocytes and hypersegmented neutrophils; prevented by folate supplementation 1-2 mg/day ^[28]^[29]
Splenomegaly and hypersplenism	Extravascular haemolysis → reticuloendothelial system hyperplasia → splenic enlargement → eventually the enlarged spleen non-selectively sequesters normal WBCs and platelets too	Cytopenias beyond what the haemolysis alone explains; may require splenectomy
Iron overload (if transfusion-dependent)	See Section 2.3 below
Chronic kidney disease	Free haemoglobin from intravascular haemolysis is directly nephrotoxic → tubular damage, haemosiderinuria → chronic tubulointerstitial injury	Rising creatinine, proteinuria; particularly in PNH
Venous thromboembolism	Free haemoglobin scavenges nitric oxide (NO) → loss of NO-mediated vasodilation and anti-platelet effects → prothrombotic state; particularly in PNH and sickle cell	DVT, PE, Budd-Chiari syndrome (especially PNH); anticoagulation needed
Leg ulcers	Microvascular occlusion + tissue hypoxia + endothelial dysfunction → chronic skin breakdown, especially over the medial malleolus	Chronic, non-healing ulcers; common in sickle cell disease, hereditary spherocytosis, thalassaemia intermedia

Aplastic anaemia has unique complications beyond the anaemia itself, because all three lineages are affected (pancytopenia):

Complication	Lineage Affected	Pathophysiology	Clinical Significance
Recurrent infections (most dangerous)	Neutropenia	ANC < 0.5 → profound immunodeficiency; bacterial infections (sepsis, pneumonia, UTI) are typical; invasive fungal infections are an important cause of death ^[20]^[21]	Needs empirical broad-spectrum antibiotics for neutropenic fever; antifungal prophylaxis
Mucocutaneous bleeding	Thrombocytopenia	Platelet < 20 × 10⁹/L → spontaneous bleeding; sites: lung (16%), GI (14%), CNS (12%) ^[37] — CNS haemorrhage can be fatal	Platelet transfusion to maintain above bleeding threshold
Clonal evolution to PNH	HSC	A PNH clone (PIGA-mutated) may emerge from the aplastic marrow — possibly because PNH cells are resistant to the T-cell mediated destruction affecting normal HSCs → selective survival advantage	Screen periodically with flow cytometry for CD55/CD59; may develop intravascular haemolysis and thrombosis
Clonal evolution to MDS or AML ^[7]	HSC	Chronic marrow stress and immune pressure select for cytogenetically abnormal clones → MDS → eventual leukaemic transformation	Monitor with regular CBC, PBS; repeat BM biopsy if cytopenias worsen or new abnormalities appear
Iron overload (transfusion-related)	N/A	See Section 2.3 below

From GC 047 lecture slides: when taking history for inherited causes of anaemia, ask about complications (including those due to long-term red cell transfusion) ^[38].

This is one of the most important long-term complications affecting chronically transfusion-dependent patients (aplastic anaemia, MDS, thalassaemia major). It deserves detailed attention.

Why does iron overload occur?

Each unit of packed RBCs contains approximately 200-250 mg of iron [35a]^[1]
Normal daily iron excretion is only ~1 mg/day [35a] — the body has no active mechanism for excreting excess iron
Normal daily iron absorption is also ~1 mg/day to maintain balance [35a]
Therefore, a patient receiving regular transfusions accumulates iron at a rate far exceeding the body's capacity to excrete it

Target organ damage from iron overload:

Transfusion haemosiderosis causes iron accumulation within: [35a]

Organ	Consequence	Pathophysiology
Liver	Liver fibrosis and HCC [35a]	Iron deposited in hepatocytes → catalyses free radical formation (Haber-Weiss reaction: Fe²⁺ + H₂O₂ → Fe³⁺ + OH• + OH⁻) → oxidative hepatocyte damage → fibrosis → cirrhosis → increased HCC risk ^[1]
Heart	Heart failure (dilated cardiomyopathy) [35a]^[1]	Iron deposits in cardiomyocytes → oxidative damage → myocyte death → progressive systolic dysfunction; cardiac iron overload is the leading cause of death in transfusion-dependent thalassaemia
Endocrine organs	Diabetes mellitus, growth retardation, hypogonadism [35a]^[1]	Iron deposits in pancreatic β-cells → β-cell destruction → DM; pituitary iron deposition → hypogonadotropic hypogonadism, growth hormone deficiency; thyroid iron → hypothyroidism
Skin	Hyperpigmentation ("bronze diabetes") ^[1]	Iron and melanin co-deposition in the dermis
Joints	Arthropathy (especially 2nd and 3rd MCP joints)	Iron deposition in synovium → chondrocalcinosis; "squared-off" bone ends and hook-like osteophytes on X-ray ^[1]

Monitoring:

Serum ferritin (target < 1000 μg/L in transfusion-dependent patients)
Liver and cardiac MRI (T2) to directly assess organ iron deposition* ^[1] — ferritin alone can be unreliable (it is a positive acute phase reactant)

Prevention and treatment:

Iron chelation therapy (deferoxamine, deferasirox, deferiprone) — see Management section
Venesection if the patient can tolerate it (not usually feasible in aplastic anaemia/MDS where the marrow is failing)

High Yield – Iron Overload as Exam Question

The Haematology Introduction to Haematological Investigations lecture slide asks: "Why is the ferritin level so high? What complications have developed? How may the management of the case be improved?" ^[39]. This is a classic question stem for thalassaemia or aplastic anaemia patients on chronic transfusion. The answer framework is: (1) high ferritin because of transfusional iron overload (each unit = 200-250 mg Fe, excretion only 1 mg/day); (2) complications = liver fibrosis/cirrhosis, cardiomyopathy, endocrinopathies (DM, hypogonadism); (3) improve management by optimising iron chelation therapy (compliance, dose adjustment, switching agents if needed).

Complication	Pathophysiology	Clinical Significance
Transformation to AML	Accumulation of genetic mutations in the dysplastic clone → blast count rises above 20% → by definition, this is AML	PMF has the highest rate of leukaemic transformation (15%), followed by PV, then ET ^[26]; in MDS specifically, higher-risk IPSS-R categories have greater transformation risk; requires intensive chemotherapy ± HSCT
Recurrent infections	Neutropenia + qualitative neutrophil dysfunction (dysplastic neutrophils function poorly even when present in adequate numbers)	Common cause of morbidity and mortality
Bleeding	Thrombocytopenia + qualitative platelet dysfunction
Iron overload	From chronic transfusion support	Same as above (Section 2.3)
Autoimmune manifestations	MDS is associated with autoimmune phenomena (vasculitis, seronegative arthritis, Sweet's syndrome, relapsing polychondritis) in ~10-20% of cases	Immune dysregulation from the abnormal clone

The macrocytosis itself has minimal direct complications. The complications are from the alcohol use and associated liver disease:

Complication	Mechanism
Alcoholic liver disease → cirrhosis	Direct hepatotoxicity of ethanol and acetaldehyde → steatosis → steatohepatitis → fibrosis → cirrhosis
Portal hypertension	Cirrhosis → increased intrahepatic resistance → oesophageal/gastric varices, splenomegaly, ascites
Variceal bleeding	Portal hypertension → collateral formation → varices → rupture → life-threatening upper GI bleed → iron deficiency anaemia superimposed on macrocytosis → dimorphic blood picture
Concurrent nutritional deficiencies	Poor diet + impaired GI absorption → thiamine deficiency (Wernicke's encephalopathy), folate deficiency (megaloblastic anaemia), vitamin K deficiency (coagulopathy)
Pancytopenia	Direct marrow suppression by alcohol; also hypersplenism from portal hypertension
Wernicke-Korsakoff syndrome	Thiamine (B1) deficiency → Wernicke's encephalopathy (acute: confusion, ataxia, ophthalmoplegia) → if untreated, Korsakoff's syndrome (chronic: confabulation, anterograde amnesia)

The macrocytic anaemia from hypothyroidism is generally mild and has few complications on its own. However:

Complication	Mechanism
Myxoedema coma (extreme)	Severe, prolonged untreated hypothyroidism → profound hypothermia, hypoventilation, altered consciousness; the anaemia worsens tissue hypoxia in this state
Pericardial effusion	Hypothyroidism causes serous effusions (pericardial, pleural, ascites) from mucopolysaccharide deposition and altered capillary permeability → pericardial effusion can further compromise cardiac output in an anaemic patient
Hyperlipidaemia and accelerated atherosclerosis	↓LDL receptor expression → ↑LDL cholesterol → accelerated CAD; combined with anaemia → ↑risk of myocardial ischaemia
Associated pernicious anaemia	Autoimmune clustering: Hashimoto's thyroiditis + pernicious anaemia → if missed, progressive B12 deficiency causes irreversible neurological damage

3. Complications of Treatment

HSCT is potentially curative but carries significant morbidity. The complications are divided into early and late ^[37]:

Early complications ( < 1 year):

Complication	Pathophysiology
Cytopenia-related: anaemia, bleeding (26% in first year, 9% life-threatening; sites: lung 16%, GI 14%, CNS 12%), neutropenic infections (bacterial and fungal) ^[37]	Marrow has not yet engrafted or is recovering
Oral mucositis	Conditioning regimen (chemo/radiation) damages rapidly dividing mucosal epithelium; managed with ice cubes, pre-treatment laser, IV palifermin ± TPN ^[37]
Veno-occlusive disease (VOD) / sinusoidal obstruction syndrome	Conditioning damages hepatic venous endothelium → fibrin deposition in sinusoids → outflow obstruction → painful hepatomegaly, ascites, jaundice ± fulminant liver failure; prophylaxis: ursodeoxycholic acid/heparin; treatment: defibrotide + supportive ^[37]
Acute graft-versus-host disease (aGvHD)	Donor T cells recognise host tissues as foreign → immune attack on skin (rash), GI tract (diarrhoea), liver (jaundice); grading I-IV
Graft rejection (host-versus-graft)	Residual host immunity rejects donor cells → graft failure

Late complications ( > 1 year):

Complication	Details
Cardiovascular disease: 5% at 5y, 9% at 15y — most common cause of morbidity and non-relapse mortality ^[37]	Due to (1) metabolic effects of immunosuppressants, (2) concurrent CV risk factors, (3) chronic GvHD
Endocrine dysfunction: T2DM (3× increased risk), hypothyroidism, hypogonadism, infertility, osteoporosis/AVN (steroid use) ^[37]	Conditioning regimen and chronic immunosuppression damage endocrine organs
Second malignancy: PTLD, post-treatment MDS/AML, solid organ tumours (SCC of skin/oral cavity) ^[37]	Immune dysregulation, prior chemo/radiation exposure
Chronic graft-versus-host disease (cGvHD) ^[37]	Affects skin (scleroderma-like), mouth (sicca, lichenoid changes), eyes (keratoconjunctivitis sicca), lungs (bronchiolitis obliterans), liver, fascia; requires prolonged immunosuppression
Cataracts ^[37]	From total body irradiation
Infections	Prolonged immunosuppression → susceptible to viral reactivation (CMV, EBV, VZV), Pneumocystis, encapsulated bacteria
Relapse of primary disease ^[37]	The original disease (aplastic anaemia, MDS, AML) may recur

Overall prognosis of HSCT ^[37]:

Allogeneic HSCT: 75% long-term survival; 80% at 15y for those surviving ≥ 2 years; 9.9× mortality of general population (highest years 2-5 post-HSCT); 29% relapse, 22% chronic GvHD
Autologous HSCT: 80% overall survival at 20y for those surviving ≥ 5 years; 4-9× mortality of general population

Complication	Mechanism
Serum sickness (from ATG)	Foreign protein (horse/rabbit serum) → immune complex formation → fever, rash, arthralgia, proteinuria; typically 7-14 days after infusion
Anaphylaxis (from ATG)	IgE-mediated hypersensitivity to foreign protein
Nephrotoxicity (from cyclosporine)	Calcineurin inhibitor → afferent arteriolar vasoconstriction → reduced GFR; also chronic tubulointerstitial fibrosis
Hypertension (from cyclosporine)	Renal vasoconstriction → sodium retention
Gingival hyperplasia, hirsutism (from cyclosporine)	Effects on fibroblast proliferation
Relapse of aplastic anaemia	If cyclosporine is tapered too rapidly, the autoimmune T-cell attack on HSCs can recur
Clonal evolution	Even after successful IST, patients remain at risk of developing PNH, MDS, or AML (the IST suppresses the immune attack but does not eliminate the underlying genetic predisposition to clonal evolution)

Relevant for patients with hereditary spherocytosis, refractory AIHA, or thalassaemia major who undergo splenectomy.

Post-splenectomy patients are at risk of life-threatening infection from encapsulated bacteria → overwhelming post-splenectomy infection (OPSI) ^[31].

Complication	Pathophysiology	Prevention
OPSI (overwhelming post-splenectomy infection)	The spleen is the primary site for clearing opsonised encapsulated bacteria (Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae type b); without it, these organisms can cause fulminant sepsis with mortality > 50%	Vaccination (PCV13 + PPSV23, meningococcal, HiB) ≥ 2 weeks before elective splenectomy; lifelong prophylactic penicillin V; patient education; MedicAlert bracelet
Reactive thrombocytosis	Spleen normally sequesters ~30% of circulating platelets; after splenectomy, platelet count rises — usually transient but can persist	Monitor; rarely requires treatment; antiplatelet therapy if very high ( > 1000 × 10⁹/L) with thrombotic risk
Spurious leukocytosis, Howell-Jolly bodies ^[31]	WBCs no longer cleared by spleen → apparent leukocytosis; nuclear remnants in RBCs (Howell-Jolly bodies) no longer pitted by splenic macrophages → visible on PBS	Expected post-splenectomy findings — NOT alarming
Portal/splenic vein thrombosis	Post-surgical thrombotic tendency + thrombocytosis	Anticoagulation if documented thrombosis

A brief mention of complications from the investigations themselves:

Investigation	Complication	Notes
Bone marrow biopsy	Pain, infection, bleeding	Complications uncommon (0.05-0.07%); most commonly pain, infection, bleeding ^[25]; thrombocytopenia is NOT a contraindication — transfuse platelets to > 20 × 10⁹/L prior
Blood transfusion	Febrile non-haemolytic reaction (3%), urticaria (1%), acute/delayed haemolytic reaction, TRALI, TACO, iron overload, alloimmunisation	See transfusion section in Management

Aetiology	Key Complications
Anaemia (all causes)	High-output cardiac failure, cardiac ischaemia, syncope, increased mortality
Haemolytic anaemia	Pigment gallstones, aplastic crisis (parvovirus B19), folate deficiency, splenomegaly/hypersplenism, iron overload (if transfusion-dependent), CKD and thrombosis (if intravascular haemolysis)
Aplastic anaemia	Life-threatening infections (bacterial, fungal), bleeding (CNS, lung, GI), clonal evolution (PNH, MDS, AML), iron overload (transfusion)
MDS	Transformation to AML, infections, bleeding, iron overload, autoimmune manifestations
Alcoholism	Liver cirrhosis, portal hypertension, variceal bleeding, nutritional deficiencies (Wernicke-Korsakoff), concurrent folate/iron deficiency
Liver disease	All complications of cirrhosis; hypersplenism; variceal bleeding causing superimposed IDA
Hypothyroidism	Accelerated atherosclerosis + anaemia → cardiac ischaemia; associated pernicious anaemia
Transfusion therapy	Iron overload (liver fibrosis/HCC, cardiomyopathy, endocrinopathies), alloimmunisation, transfusion reactions
HSCT	Early: mucositis, VOD, aGvHD, infections. Late: CVD, endocrine dysfunction, second malignancies, cGvHD, cataracts
Splenectomy	OPSI from encapsulated bacteria, reactive thrombocytosis, portal vein thrombosis

High Yield Summary — Complications

Anaemia itself causes high-output cardiac failure, cardiac ischaemia, and increased mortality — these are predictable consequences of tissue hypoxia and compensatory cardiovascular overload.
Chronic haemolysis → pigment gallstones (cholecystectomy if symptomatic), folate depletion (supplement 1-2 mg/day), aplastic crisis from parvovirus B19, splenomegaly.
Aplastic anaemia → life-threatening infections (most dangerous complication), bleeding, and clonal evolution (PNH, MDS, AML) — screen periodically.
Transfusional iron overload is the most important long-term complication of chronic transfusion. Each unit = 200-250 mg Fe; excretion only 1 mg/day. Target organs: liver (fibrosis, HCC), heart (cardiomyopathy — leading cause of death in transfusion-dependent thalassaemia), endocrine (DM, hypogonadism). Manage with iron chelation (deferoxamine, deferasirox, deferiprone) and MRI monitoring.
MDS → transformation to AML is the most feared complication; higher IPSS-R risk category = higher transformation risk.
Post-splenectomy → overwhelming post-splenectomy infection (OPSI) from encapsulated bacteria; prevent with vaccinations + prophylactic penicillin + patient education.
HSCT complications: early (mucositis, VOD, aGvHD, infections), late (CVD — most common cause of non-relapse mortality, endocrine dysfunction, second malignancies, cGvHD).

Active Recall – Complications of Non-Megaloblastic Anaemia

High Yield Summary

Non-Megaloblastic Macrocytic Anaemia — Key Points:

Definition: Macrocytic anaemia (MCV > 100 fL) NOT caused by B12/folate deficiency or impaired DNA synthesis. Caused by membrane lipid abnormalities, reticulocytosis, or marrow failure/dysplasia.
PBS hallmark: Round macrocytes with normal neutrophils (vs. oval macrocytes + hypersegmented neutrophils in megaloblastic).
Most common cause: Alcoholism — direct toxic effect on erythroid membrane + altered lipid metabolism ± associated liver disease.
Main causes (exam list): Alcoholism, liver disease, hypothyroidism, haemolytic anaemia (reticulocytosis), aplastic anaemia, MDS.
Aplastic anaemia: Pancytopenia from BM hypoplasia; 70-80% idiopathic (T-cell mediated); hepatitis is a well-known preceding infection; BM biopsy shows hypocellular marrow with > 90% fat.
MDS: Clonal dysplastic haematopoiesis; median age ~65; may transform to AML; NO hepatosplenomegaly.
Investigation approach: PBS morphology → reticulocyte count → if high: haemolytic screen; if low/normal: LFT, TFT, alcohol history → if all normal: bone marrow biopsy (for aplastic anaemia or MDS).
Pathophysiology of membrane-mediated macrocytosis: Excess free cholesterol from dysregulated lipoprotein metabolism → deposits into RBC membrane → increases surface area → round macrocytes.

High Yield Summary — Differential Diagnosis of Non-Megaloblastic Anaemia

Always exclude megaloblastic anaemia first — check B12/folate; MCV > 120 fL is almost exclusively megaloblastic or chemotherapy-related.
The reticulocyte count bifurcates the differential: HIGH → haemolysis/blood loss recovery; LOW/NORMAL → liver disease, hypothyroidism, alcoholism, aplastic anaemia, MDS.
Most common cause overall: alcoholism (direct toxicity + membrane lipid changes).
In HK: liver disease (chronic HBV → cirrhosis) and G6PD-related haemolysis are particularly relevant.
Aplastic anaemia vs MDS: both cause pancytopenia with macrocytosis; aplastic anaemia has hypocellular marrow with morphologically NORMAL cells; MDS has dysplastic cells ± cytogenetic abnormalities.
ACD is typically normocytic but is a key differential in any anaemic patient with chronic disease; distinguished from IDA by TIBC (high in IDA, low in ACD) and ferritin (low in IDA, high in ACD).
Always take a thorough drug history — many drugs cause macrocytosis.

High Yield Summary — Diagnostics

Non-megaloblastic macrocytic anaemia is diagnosed by: MCV > 100, round macrocytes + normal neutrophils on PBS, normal B12/folate.
Reticulocyte count is the key branching investigation: elevated → haemolysis workup; low/normal → LFT, TFT, alcohol history → if all normal, BM biopsy.
Aplastic anaemia requires BM trephine biopsy for diagnosis: hypocellular marrow (< 25% cellularity), fat replacement, morphologically normal residual cells, no fibrosis/malignancy. Always exclude PNH (flow cytometry for CD55/CD59) and Fanconi anaemia (DEB test in children).
MDS requires BM biopsy + cytogenetics: dysplastic morphology, blast count < 20%, ring sideroblasts, characteristic cytogenetic abnormalities. Always check B12/folate first.
Ferritin is the most sensitive and specific marker for iron deficiency, but is a positive acute phase reactant → can be falsely normal/elevated in inflammation. TIBC is the most useful single test to distinguish IDA from ACD.
MCV > 110-115 fL is almost exclusively megaloblastic — if you see this, think B12 deficiency or chemotherapy before non-megaloblastic causes.

High Yield Summary — Management

General principle: Non-megaloblastic macrocytic anaemia management = treat the underlying cause + supportive care.
Alcoholism: cessation → MCV normalises in 2-4 months.
Liver disease: treat the liver disease; macrocytosis improves with disease control.
Hypothyroidism: levothyroxine; Hb/MCV normalises in 3-6 months.
Haemolytic anaemia: folate supplementation for all; cause-specific (steroids for AIHA, avoid triggers for G6PD, splenectomy for HS, eculizumab for PNH).
Aplastic anaemia: First line for young patients with HLA-matched sibling = allogeneic HSCT. Otherwise: ATG + CsA ± eltrombopag (triple immunosuppression). Supportive: transfusion, chelation, G-CSF, antibiotics. Screen for PNH/MDS/AML.
MDS: Risk-stratified. Low risk: monitor ± ESA ± targeted therapy (lenalidomide for del(5q), luspatercept for MDS-RS). High risk: allogeneic HSCT or intensive chemo. HMA (azacitidine) for intermediate risk.
Iron chelation: Start when ferritin > 1000 μg/L; options: deferoxamine (SC), deferasirox (PO), deferiprone (PO).
Post-splenectomy: vaccinate against encapsulated organisms, lifelong prophylactic penicillin, patient education.

High Yield Summary — Complications

Anaemia itself causes high-output cardiac failure, cardiac ischaemia, and increased mortality — these are predictable consequences of tissue hypoxia and compensatory cardiovascular overload.
Chronic haemolysis → pigment gallstones (cholecystectomy if symptomatic), folate depletion (supplement 1-2 mg/day), aplastic crisis from parvovirus B19, splenomegaly.
Aplastic anaemia → life-threatening infections (most dangerous complication), bleeding, and clonal evolution (PNH, MDS, AML) — screen periodically.
Transfusional iron overload is the most important long-term complication of chronic transfusion. Each unit = 200-250 mg Fe; excretion only 1 mg/day. Target organs: liver (fibrosis, HCC), heart (cardiomyopathy — leading cause of death in transfusion-dependent thalassaemia), endocrine (DM, hypogonadism). Manage with iron chelation (deferoxamine, deferasirox, deferiprone) and MRI monitoring.
MDS → transformation to AML is the most feared complication; higher IPSS-R risk category = higher transformation risk.
Post-splenectomy → overwhelming post-splenectomy infection (OPSI) from encapsulated bacteria; prevent with vaccinations + prophylactic penicillin + patient education.
HSCT complications: early (mucositis, VOD, aGvHD, infections), late (CVD — most common cause of non-relapse mortality, endocrine dysfunction, second malignancies, cGvHD).

Non-megaloblastic Anaemia

Non-Megaloblastic Anaemia

3. Anatomy and Function: The Red Blood Cell Membrane

4. Aetiology (Hong Kong Focus) and Pathophysiology

6. Clinical Features

6.1 Symptoms

6.2 Signs

8. Special Topics Relevant to Non-Megaloblastic Anaemia

Active Recall – Non-Megaloblastic Anaemia

Differential Diagnosis of Non-Megaloblastic Macrocytic Anaemia

Level 2: Differential Diagnosis Among Non-Megaloblastic Causes

Active Recall – Differential Diagnosis of Non-Megaloblastic Anaemia

References

Key Concept: Non-Megaloblastic Macrocytic Anaemia Is a Syndrome, Not a Single Disease

1. Diagnostic Criteria

1.2 Formal Diagnostic Criteria for Specific Underlying Causes

3. Investigation Modalities — Detailed Interpretation

3.10 Specialised Investigations

Active Recall – Diagnostics of Non-Megaloblastic Anaemia

Overarching Principle: Treat the Underlying Cause

2. General Supportive Management (Applies to All Causes)

3. Cause-Specific Management

3.4 Haemolytic Anaemia

3.5 Aplastic Anaemia

3.6 Myelodysplastic Syndrome (MDS)

Active Recall – Management of Non-Megaloblastic Anaemia

1. Complications of the Anaemia Itself

2. Complications Specific to Underlying Causes

3. Complications of Treatment

Active Recall – Complications of Non-Megaloblastic Anaemia

On this page

Non-megaloblastic Anaemia

Non-Megaloblastic Anaemia

1. Definition

2. Epidemiology and Risk Factors

3. Anatomy and Function: The Red Blood Cell Membrane

3.1 Normal RBC Membrane

3.2 How Membrane Lipid Abnormalities Cause Macrocytosis

3.3 Why Reticulocytes Are Larger

4. Aetiology (Hong Kong Focus) and Pathophysiology

4.1 Alcoholism (Most Common Cause) [1]

4.2 Liver Disease [3][4]

4.3 Hypothyroidism [1]

4.4 Haemolytic Anaemia (Reticulocytosis) [1][3][4]

4.5 Aplastic Anaemia [3][4][5][7]

4.6 Myelodysplastic Syndrome (MDS) [3][4][7]

4.7 Other / Less Common Causes

5. Classification

6. Clinical Features

6.1 Symptoms

A. Symptoms of Anaemia (General — Common to All Anaemias)

B. Symptoms Specific to Underlying Cause

6.2 Signs

A. Signs of Anaemia (General)

B. Signs Specific to Underlying Cause

6.3 Key PBS Morphology Clues

7. Approach to Non-Megaloblastic Macrocytic Anaemia — Linking It All Together

8. Special Topics Relevant to Non-Megaloblastic Anaemia

8.1 Pure Red Cell Aplasia (PRCA) [5]

8.2 Sideroblastic Anaemia

8.3 Luspatercept in MDS [9]

Active Recall – Non-Megaloblastic Anaemia

References

Differential Diagnosis of Non-Megaloblastic Macrocytic Anaemia

Level 1: Excluding Megaloblastic Anaemia

Level 2: Differential Diagnosis Among Non-Megaloblastic Causes

Differential 1: Alcoholism (Most Common Cause) [1]

Differential 2: Chronic Liver Disease [3][4]

Differential 3: Hypothyroidism [1]

Differential 4: Haemolytic Anaemia [1][3][4][14][15]

Differential 5: Aplastic Anaemia [3][4][5][7][16]

Differential 6: Myelodysplastic Syndrome (MDS) [1][3][4][7][13]

Differential 7: Drug-Induced Macrocytosis

Differential 8: Other / Less Common Causes

Approach to Distinguishing Anaemia of Chronic Disease (ACD) — A Normocytic Mimicker

Summary Differential Diagnosis Table

Key Differentials That Can Mimic Non-Megaloblastic Macrocytic Anaemia

Active Recall – Differential Diagnosis of Non-Megaloblastic Anaemia

References

Diagnostic Criteria, Algorithm, and Investigation Modalities for Non-Megaloblastic Macrocytic Anaemia

Key Concept: Non-Megaloblastic Macrocytic Anaemia Is a Syndrome, Not a Single Disease

1. Diagnostic Criteria

1.1 Criteria to Establish Non-Megaloblastic Macrocytic Anaemia

1.2 Formal Diagnostic Criteria for Specific Underlying Causes

A. Aplastic Anaemia — Severity Classification [5][7][20][21]

B. Myelodysplastic Syndrome (MDS) — WHO/ICC Classification Principles [7][13]

C. Haemolytic Anaemia — No Single Diagnostic Criterion

D. Liver Disease, Hypothyroidism, Alcoholism

2. Diagnostic Algorithm

3. Investigation Modalities — Detailed Interpretation

3.1 Complete Blood Count (CBC) with Indices

3.2 Peripheral Blood Smear (PBS)

3.3 Serum B12 and Folate Levels

3.4 Reticulocyte Count

3.5 Haemolytic Screen

3.6 Liver Function Tests (LFT)

3.7 Thyroid Function Tests (TFT)

3.8 Iron Profile

3.9 Bone Marrow Examination

3.10 Specialised Investigations

Flow Cytometry

Chromosome Breakage Analysis (DEB Test)

Cytogenetics and Molecular Genetics

Other Specific Tests

4. Summary of Diagnostic Approach — Step-by-Step

Active Recall – Diagnostics of Non-Megaloblastic Anaemia

References

Management of Non-Megaloblastic Macrocytic Anaemia

Overarching Principle: Treat the Underlying Cause

1. Management Algorithm — Overview

2. General Supportive Management (Applies to All Causes)