1. Classification of Haemolysis

•    Intravascular haemolysis:

o    RBCs destroyed within blood vessels

o    Examples:

    Paroxysmal nocturnal haemoglobinuria (PNH)

    Microangiopathic haemolytic anaemia (MAHA: TTP, HUS, DIC, HELLP)

    Paroxysmal cold autoimmune haemolytic anaemia

    Acute G6PD crisis

•    Extravascular haemolysis:

o    RBCs destroyed in the spleen and liver by macrophages

o    Examples:

    Hereditary spherocytosis

    Warm autoimmune haemolytic anaemia

    Pyruvate kinase deficiency

    Delayed haemolytic transfusion reactions

•    Mixed or variable:

o    Sickle cell disease

o    β-thalassaemia major (transfusion-related haemolysis)

o    Chronic low-grade G6PD deficiency

2. Laboratory Features in Haemolysis

•    Common to both intravascular and extravascular:

o    Anaemia (↓ Hb)

o    Reticulocytosis (↑ reticulocyte count)

o    ↑ Lactate dehydrogenase (LDH)

o    ↑ Unconjugated bilirubin

•    Specific to intravascular haemolysis:

o    ↓ or undetectable haptoglobin

o    Haemoglobinaemia

o    Haemoglobinuria (dark urine)

o    Haemosiderinuria (several days after haemolysis)

•    Predominantly seen in extravascular haemolysis:

o    Splenomegaly

o    Spherocytes on blood film

o    Normal or only mildly reduced haptoglobin

o    No haemoglobinuria

3. Hereditary Spherocytosis and Membrane Disorders

•    Autosomal dominant inheritance

•    Defect in RBC membrane proteins (spectrin, ankyrin)

•    Features: jaundice, splenomegaly, gallstones

•    Blood film: spherocytes, ↑ MCHC

•    Diagnosis: EMA-binding test (preferred), osmotic fragility test (historical)

•    Treatment: folate supplementation, splenectomy in severe cases

4. Enzyme Deficiencies

•    G6PD deficiency:

o    X-linked recessive

o    Triggered by infection, fava beans, drugs (sulfa, dapsone, nitrofurantoin, antimalarials)

o    Episodic intravascular haemolysis

o    Blood film: Heinz bodies (oxidised Hb), bite cells

•    Pyruvate kinase deficiency:

o    Autosomal recessive

o    Chronic extravascular haemolysis

o    Neonatal jaundice, splenomegaly

o    ↑ 2,3-BPG → facilitates oxygen unloading

5. Autoimmune Haemolytic Anaemia (AIHA)

•    Warm AIHA:

o    IgG-mediated

o    Extravascular (splenic macrophage clearance)

o    Causes: idiopathic, SLE, CLL, drugs (penicillin, methyldopa)

o    Blood film: spherocytes

o    Positive direct Coombs’ test

o    Treatment: steroids → immunosuppressants → splenectomy

•    Cold AIHA:

o    IgM-mediated with complement activation

o    Intravascular haemolysis

o    Triggered by cold exposure, Mycoplasma, EBV, lymphomas

o    Features: acrocyanosis, haemoglobinuria in cold weather

o    Treatment: keep warm, rituximab

6. Coombs’ (Antiglobulin) Test

•    Direct Coombs’ test (DAT):

o    Detects antibodies (IgG or complement) on patient’s RBCs

o    Positive in warm AIHA (IgG), cold AIHA (C3), haemolytic transfusion reactions

•    Indirect Coombs’ test:

o    Detects free antibodies in patient serum

o    Used in crossmatching and antenatal screening

7. Paroxysmal Nocturnal Haemoglobinuria (PNH)

•    Acquired mutation affecting GPI-anchored proteins (CD55, CD59) on RBCs

•    Increased susceptibility to complement-mediated intravascular lysis

•    Features:

o    Episodic dark urine (haemoglobinuria, especially at night/morning)

o    Pancytopenia

o    Thrombosis (hepatic, cerebral veins)

•    Diagnosis: flow cytometry (absent CD55/CD59 on blood cells)

•    Treatment: eculizumab (C5 inhibitor), anticoagulation, stem cell transplant

8. Microangiopathic Haemolytic Anaemia (MAHA)

•    Intravascular haemolysis due to mechanical damage in microvasculature

•    Causes:

o    Thrombotic thrombocytopenic purpura (TTP): ↓ ADAMTS13

o    Haemolytic uraemic syndrome (HUS): often E. coli O157:H7

o    Disseminated intravascular coagulation (DIC)

o    HELLP syndrome in pregnancy

•    Blood film: schistocytes (fragmented RBCs)

•    Treatment:

o    TTP: urgent plasma exchange

o    HUS: supportive care ± eculizumab

o    DIC: treat underlying cause, give FFP/cryoprecipitate as needed

9. Sickle Cell Disease

•    Autosomal recessive β-globin mutation: glutamic acid → valine

•    HbS polymerises when deoxygenated → sickling and vaso-occlusion

•    Type of haemolysis: predominantly extravascular, some intravascular during crises

•    Types of crises:

o    Vaso-occlusive (pain)

o    Aplastic (e.g. parvovirus B19)

o    Sequestration (splenic pooling)

o    Haemolytic

•    Complications: autosplenectomy, osteomyelitis (Salmonella), stroke, priapism

•    Diagnosis: haemoglobin electrophoresis

•    Treatment: hydroxyurea, folic acid, vaccination, analgesia, transfusion as needed

10. Clinical Approach to Suspected Haemolysis

•    Check full blood count, reticulocyte count, LDH, bilirubin, haptoglobin

•    Examine blood film for spherocytes, schistocytes, bite cells

•    Use Coombs’ test to detect autoimmune cause

•    Consider urine dip for haemoglobinuria (intravascular haemolysis)

•    Look for splenomegaly on exam (suggests extravascular haemolysis)