Haemolytic Anaemias
Pathology · Haematology · lean revision notes
Haemolytic Anaemias
Haemolytic anaemias are a group of disorders in which red cell lifespan is shortened (normal ~120 days) such that bone marrow compensatory erythropoiesis cannot keep pace. They are a perennial NEET PG favourite because the lab triad, the peripheral smear morphology, and the enzyme-deficiency vignettes lend themselves beautifully to image-based and "single-best-answer" questions.
Definition & the core concept
Haemolysis = premature destruction of red blood cells. Haemolytic anaemia results only when destruction outpaces the marrow's ~6–8 fold expandable capacity. If the marrow keeps up, the patient has compensated haemolysis (raised reticulocytes, normal Hb).
Two fundamental axes are used to classify (and both are tested):
- Site of destruction → Intravascular vs Extravascular.
- Origin of defect → Intrinsic (intracorpuscular) vs Extrinsic (extracorpuscular).
High-yield: A useful rule — intrinsic = inherited (except PNH, which is acquired but intrinsic), and extrinsic = acquired (except the rare hereditary microangiopathies).
Intravascular vs Extravascular haemolysis
| Feature | Intravascular | Extravascular |
|---|---|---|
| Site | Within circulation | Spleen / liver macrophages (RES) |
| Haptoglobin | Markedly ↓ / absent | Mildly ↓ or normal |
| Free plasma Hb | ↑↑ | Normal/mild ↑ |
| Haemoglobinuria | Present | Absent |
| Haemosiderinuria | Present (days later) | Absent |
| Urine | Red/cola-coloured | Normal |
| Spleen | Usually normal | Splenomegaly |
| Classic causes | PNH, G6PD crisis, ABO mismatch, MAHA, march haemoglobinuria, clostridial sepsis | Hereditary spherocytosis, warm AIHA, hypersplenism |
High-yield: Haemosiderinuria is the marker of chronic intravascular haemolysis — iron-laden tubular cells are shed into urine days after the event (Prussian blue stain positive). It is the classic clue for PNH and chronic mechanical haemolysis.
The universal laboratory signature
Whatever the cause, haemolysis produces a recognisable biochemical pattern. Memorise this — it is the single most repeated MCQ stem.
↑ Reticulocytes → ↑ Unconjugated (indirect) bilirubin → ↑ LDH → ↓ Haptoglobin → ↑ Urinary/faecal urobilinogen.
| Marker | Direction | Why |
|---|---|---|
| Reticulocyte count | ↑ (corrected >2–3%) | Marrow compensation |
| Indirect bilirubin | ↑ | Haem catabolism (unconjugated) |
| LDH | ↑ | Released from lysed RBCs |
| Haptoglobin | ↓↓ | Binds free Hb, then cleared |
| Urine haemosiderin | + (chronic IV) | Tubular iron shedding |
| Direct Coombs (DAT) | + in immune causes | Antibody/complement on RBC |
High-yield: The combination ↑LDH + ↓haptoglobin has ~90% specificity for haemolysis; ↑LDH + low haptoglobin + raised retics essentially confirms it. Haptoglobin <25 mg/dL strongly suggests intravascular haemolysis.
A normocytic/macrocytic anaemia (macrocytosis from reticulocytosis), elevated MCHC in spherocytosis, and polychromasia on smear round out the picture.
INTRINSIC (intracorpuscular) defects
These are subdivided into membrane, enzyme, and haemoglobin defects.
1. Membrane defects — Hereditary Spherocytosis (HS)
- Most common inherited haemolytic anaemia in Northern Europeans; autosomal dominant (75%).
- Defect in vertical cytoskeleton linkages: ankyrin (most common), spectrin (α/β), band 3, protein 4.2.
- Loss of membrane surface area → loss of biconcavity → spherocytes → trapped and destroyed in splenic cords (extravascular).
Clinical: anaemia, jaundice, splenomegaly, pigment gallstones, aplastic crisis with Parvovirus B19.
Diagnosis:
- Smear: spherocytes, ↑ MCHC (hyperchromic, classic), polychromasia.
- Osmotic fragility test ↑ (best after incubation) — classic but being replaced.
- EMA (eosin-5-maleimide) binding test by flow cytometry → investigation of choice now (binds band 3; reduced fluorescence).
- Coombs negative (distinguishes from AIHA, which also has spherocytes).
High-yield: Spherocytes + negative DAT = hereditary spherocytosis. Spherocytes + positive DAT = warm autoimmune haemolytic anaemia. This single discriminator is gold for MCQs.
Management: folate supplementation; splenectomy for moderate–severe disease (after age 5–6, with pneumococcal/meningococcal/Hib vaccination + penicillin prophylaxis). Cholecystectomy if symptomatic stones.
Hereditary elliptocytosis (spectrin self-association defect, horizontal) usually milder; pyropoikilocytosis is its severe variant.
2. Enzyme defects
G6PD deficiency — the exam darling
- X-linked recessive → affects males; most common enzymopathy worldwide.
- G6PD generates NADPH → maintains reduced glutathione (GSH) → protects against oxidative stress. Deficiency → oxidised Hb precipitates as Heinz bodies → splenic "bite cells/blister cells" → episodic intravascular + extravascular haemolysis.
Triggers — remember the mnemonic for oxidants:
Mnemonic ("Stress makes G6PD pop"): Infections (commonest trigger), Fava beans (favism — Mediterranean variant), Drugs: primaquine, dapsone, sulfonamides, nitrofurantoin, methylene blue, rasburicase, naphthalene (mothballs).
Variants: African (A−) = mild, self-limited (older cells lysed); Mediterranean = severe.
Diagnosis:
- Smear: bite cells, blister cells, Heinz bodies (supravital stain — crystal violet).
- G6PD enzyme assay = investigation of choice → but measure when stable, NOT during acute crisis (reticulocytes have high G6PD → false-normal).
High-yield: Neonatal jaundice + drug-induced haemolysis + bite cells = G6PD. Always recheck the assay 2–3 months after a crisis.
Management: avoid triggers; transfuse if severe. Never give the offending drug.
Pyruvate kinase (PK) deficiency
- Autosomal recessive; most common glycolytic (Embden–Meyerhof) enzyme defect → ↓ ATP → rigid RBC → extravascular haemolysis.
- Echinocytes/burr cells; 2,3-BPG rises → right-shifted O₂ curve → symptoms milder than degree of anaemia. No response to splenectomy is partial. Mitapivat (PK activator) is newer therapy.
3. Haemoglobinopathies
Sickle cell disease (HbS)
- Point mutation: β-globin glutamate → valine at position 6 (β6 Glu→Val). Autosomal recessive.
- Deoxygenated HbS polymerises → sickling → vaso-occlusion + chronic haemolysis (both intra- and extravascular).
Crises: vaso-occlusive (painful), acute chest syndrome (leading cause of death), splenic sequestration, aplastic (Parvovirus B19), haemolytic. Autosplenectomy → encapsulated organism infections (esp. Salmonella osteomyelitis, pneumococcal sepsis).
Diagnosis: Hb electrophoresis / HPLC (investigation of choice) — HbS band; sickling test (sodium metabisulfite) and solubility test screen. Smear: sickle cells, target cells, Howell-Jolly bodies (hyposplenism).
Management: hydroxyurea (↑ HbF — drug of choice for prevention), hydration, analgesia, vaccination, penicillin prophylaxis; transfusion/exchange for severe crises; L-glutamine, crizanlizumab, voxelotor newer agents; allogeneic HSCT/gene therapy curative.
High-yield: Hydroxyurea works by raising HbF, reducing crises, ACS, and transfusion need. HbF also protects neonates — symptoms begin after ~6 months as HbF declines.
Thalassaemias
- Quantitative defect: ↓ synthesis of α (deletion) or β (point mutation) globin chains → imbalance → ineffective erythropoiesis + haemolysis.
| Type | Defect | Notes |
|---|---|---|
| β-thalassaemia major (Cooley) | ↓↓ β-chain | Transfusion-dependent, ↑ HbF & HbA2, "crew-cut" skull, hepatosplenomegaly, chipmunk facies |
| β-thal minor (trait) | 1 gene | Mild microcytic anaemia, ↑ HbA2 (>3.5%) — diagnostic |
| α-thal (HbH disease) | 3 genes deleted | HbH (β4) inclusions |
| α-thal (Hydrops fetalis, Hb Barts) | 4 genes deleted | γ4, incompatible with life |
Smear: microcytic hypochromic, target cells, basophilic stippling, nucleated RBCs. Investigation of choice: HPLC/electrophoresis (↑HbA2 in β-trait). Management: regular transfusion + iron chelation (deferasirox/deferoxamine/deferiprone); HSCT curative.
High-yield: β-thal trait vs iron-deficiency anaemia — Mentzer index = MCV/RBC count. <13 → thalassaemia** (high RBC count), **>13 → iron deficiency. RDW is normal in thal trait, high in IDA.
PNH — the acquired intrinsic defect
- Acquired clonal mutation in PIGA gene → deficiency of GPI anchor → loss of complement regulators CD55 (DAF) and CD59 (MIRL) → complement-mediated intravascular haemolysis.
- Triad: haemolysis + pancytopenia + thrombosis (esp. hepatic/Budd-Chiari, intra-abdominal veins).
- Diagnosis of choice: flow cytometry for CD55/CD59 (and FLAER). (Old Ham's acid test/sucrose lysis now obsolete.)
- Treatment: eculizumab/ravulizumab (anti-C5); iron/folate; HSCT for marrow failure.
High-yield: Morning haemoglobinuria + venous thrombosis + pancytopenia + Coombs negative intravascular haemolysis → PNH → confirm by flow cytometry (CD55/CD59).
EXTRINSIC (extracorpuscular) causes
Autoimmune haemolytic anaemia (AIHA)
DAT (direct Coombs) positive. Two clinically vital types:
| Feature | Warm AIHA | Cold AIHA (cold agglutinin disease) |
|---|---|---|
| Antibody | IgG | IgM |
| Optimal temp | 37°C | 4°C / <30°C |
| Site of lysis | Extravascular (spleen) | Intravascular (complement) + liver |
| DAT pattern | IgG ± C3 | C3d only |
| Smear | Spherocytes | Agglutination/rouleaux, RBC clumps |
| Causes | Idiopathic, SLE, CLL, methyldopa, penicillin | Mycoplasma, EBV (infectious mono), lymphoma |
| Treatment | Steroids first line, rituximab, splenectomy | Avoid cold; rituximab; steroids/splenectomy poor |
High-yield: Cold agglutinin disease following Mycoplasma pneumoniae → anti-I antibody; infectious mononucleosis (EBV) → anti-i antibody. Paroxysmal cold haemoglobinuria → Donath-Landsteiner antibody (biphasic IgG anti-P), classically post-viral in children/old syphilis.
Microangiopathic haemolytic anaemia (MAHA)
Mechanical shearing across fibrin strands/abnormal vessels → schistocytes (helmet cells, fragments) + thrombocytopenia.
Approach (TMA workup): anaemia + thrombocytopenia + schistocytes → think TTP/HUS/DIC →
- Check coagulation (PT/aPTT) → normal in TTP & HUS, deranged in DIC.
- Pentad for TTP: Fever, Anaemia (MAHA), Thrombocytopenia, Renal, Neurological (mnemonic "FAT RN"). Caused by ADAMTS13 deficiency (<10%) → ultra-large vWF multimers.
- HUS: triad of MAHA + thrombocytopenia + acute kidney injury; children, E. coli O157:H7 Shiga toxin, bloody diarrhoea.
High-yield: TTP treatment = plasma exchange (PLEX) — do NOT give platelets (fuels thrombosis); add steroids, caplacizumab, rituximab. ADAMTS13 <10% confirms TTP. HUS is largely supportive; atypical HUS → eculizumab.
Infections
- Malaria (intravascular + extravascular; blackwater fever = massive haemoglobinuria, P. falciparum).
- Babesiosis (Maltese cross on smear), Clostridium perfringens sepsis (lecithinase → fulminant intravascular haemolysis, spherocytes).
Mechanical / other
- Prosthetic (mechanical) heart valves, march haemoglobinuria, aortic stenosis → schistocytes.
- Hypersplenism, Wilson's disease (copper-induced Coombs-negative haemolysis), Zieve syndrome (alcoholic + hyperlipidaemia + haemolysis with spur cells).
Peripheral smear — the image-question goldmine
| Morphology | Points to |
|---|---|
| Spherocytes | HS, warm AIHA |
| Bite/blister cells, Heinz bodies | G6PD deficiency |
| Sickle cells | Sickle cell disease |
| Target cells | Thalassaemia, HbC, liver disease |
| Schistocytes/helmet cells | MAHA (TTP/HUS/DIC), valve haemolysis |
| Echinocytes (burr) | PK deficiency, uraemia |
| Spur cells (acanthocytes) | Liver disease, abetalipoproteinaemia, Zieve |
| Agglutination / rouleaux | Cold agglutinin disease |
| Howell-Jolly bodies | Hyposplenism, post-splenectomy |
| Basophilic stippling | Thalassaemia, lead poisoning, sideroblastic |
| Maltese cross | Babesiosis |
Stepwise diagnostic approach
Step 1 → Confirm haemolysis: ↑retics, ↑LDH, ↑indirect bilirubin, ↓haptoglobin. Step 2 → Intravascular or extravascular? check haemoglobinuria, haemosiderinuria, splenomegaly. Step 3 → Direct Coombs (DAT): Positive → immune (AIHA); Negative → non-immune. Step 4 → If DAT negative: examine smear → spherocytes (HS/EMA test), schistocytes (TMA/coag screen), bite cells (G6PD assay), sickle cells (HPLC), targets/stippling (HPLC for thal). Step 5 → Specific confirmatory test: EMA flow / G6PD assay / Hb HPLC / flow cytometry CD55-59 / ADAMTS13.
High-yield: The Direct Antiglobulin (Coombs) Test is the single most important branch point — it instantly separates immune from non-immune haemolysis.
Complications (cross-cutting)
- Pigment (bilirubinate) gallstones — any chronic haemolysis.
- Folate deficiency from hyperproliferation → megaloblastic crisis.
- Aplastic crisis with Parvovirus B19 (HS, sickle, thalassaemia).
- Iron overload — from transfusions (thal major) → cardiac/hepatic siderosis.
- Pulmonary hypertension (chronic intravascular haemolysis — NO scavenging by free Hb).
- Thrombosis (PNH, PCH, sickle).
Key differentials to nail
- Haemolytic vs blood-loss anaemia: both raise retics, but only haemolysis raises LDH/bilirubin and lowers haptoglobin.
- Spherocytosis vs warm AIHA: DAT.
- β-thal trait vs IDA: Mentzer index, RDW, ferritin, HbA2.
- TTP vs HUS vs DIC: coagulation profile + neuro vs renal predominance + ADAMTS13.
- G6PD assay timing: false-normal during crisis.
Recently asked / exam angle
- EMA binding test has overtaken osmotic fragility as the modern investigation of choice for HS — frequently tested as "newer diagnostic test."
- Mentzer index numeric cut-off (<13 thalassaemia) is a recurring one-liner.
- Image-based smear questions: bite cells (G6PD), schistocytes (MAHA), Maltese cross (Babesia), basophilic stippling (lead/thal).
- "Do not transfuse platelets in TTP" and "PLEX is treatment of choice" are repeatedly examined.
- CD55/CD59 by flow cytometry as the test of choice for PNH (replacing Ham's test).
- Anti-I (Mycoplasma) vs anti-i (EBV) matching questions.
- β6 Glu→Val mutation in sickle cell — direct molecular question.
- Drug list for G6PD oxidant haemolysis (primaquine, dapsone, nitrofurantoin, rasburicase).
- Hydroxyurea raising HbF — mechanism question.
Rapid revision
- Haemolysis triad: ↑LDH, ↑indirect bilirubin, ↓haptoglobin, ↑reticulocytes.
- Haemosiderinuria = chronic intravascular haemolysis (PNH).
- DAT positive → immune; negative → non-immune — the key branch point.
- Spherocytes + negative Coombs = HS; + positive Coombs = warm AIHA.
- HS investigation of choice now = EMA binding (flow cytometry); classic = osmotic fragility; smear shows ↑MCHC.
- G6PD = X-linked, bite cells + Heinz bodies; assay false-normal in crisis.
- Sickle cell = β6 Glu→Val; hydroxyurea ↑HbF; HPLC is diagnostic.
- **Mentzer index <13 → thalassaemia**, >13 → iron deficiency; β-trait shows ↑HbA2.
- PNH = ↓CD55/CD59 (GPI anchor, PIGA gene); flow cytometry diagnostic; eculizumab Rx.
- TTP = ADAMTS13 <10%, pentad FAT RN, treat with plasma exchange — never platelets.
- Cold agglutinins: anti-I = Mycoplasma, anti-i = EBV; Donath-Landsteiner = PCH (biphasic anti-P).
- Schistocytes = MAHA; check coagulation to separate TTP/HUS (normal) from DIC (deranged).