Master Haematology
for PLAB 1

What the PLAB 1 Tests in Haematology

PLAB 1 Haematology tests your ability to recognise and manage common blood disorders in a UK clinical context. You must interpret full blood count (FBC) and coagulation profiles, identify microcytic (iron deficiency, thalassaemia trait) versus macrocytic (B12/folate deficiency, alcohol) anaemias, and differentiate haemolytic anaemias (autoimmune, G6PD deficiency, sickle cell disease). You need to know diagnostic cut-offs (Hb <130 g/L men, <120 g/L women; MCV <80 fL microcytic, >100 fL macrocytic), first-line treatments (oral iron, IM B12, folic acid), and when to refer for urgent haematology opinion (e.g., suspected acute leukaemia, pancytopenia, or DIC). The exam emphasises decision-making in anaemia of chronic disease, anticoagulation management (warfarin, DOACs, LMWH), and recognising transfusion reactions and complications (e.g., iron overload, anaphylaxis). You will also be tested on bleeding disorders (haemophilia A/B, von Willebrand disease) and thrombophilia (factor V Leiden, antiphospholipid syndrome).

High-Yield Concepts

• Iron deficiency anaemia (IDA): Microcytic (MCV <80 fL), hypochromic anaemia. Ferritin <15 ng/mL is diagnostic. First-line: oral ferrous sulphate 200 mg TDS (or ferrous fumarate/gluconate). Check for GI bleeding in men and postmenopausal women (OGD + colonoscopy). Response: Hb rise >10 g/L in 2-4 weeks. IV iron (ferric carboxymaltose) if intolerant or severe.
• Vitamin B12 deficiency anaemia: Macrocytic (MCV >100 fL) with possible neurological symptoms (peripheral neuropathy, subacute combined degeneration of the cord). Causes: pernicious anaemia (anti-intrinsic factor antibodies, anti-parietal cell antibodies), vegan diet, gastrectomy. Treatment: hydroxocobalamin 1 mg IM three times weekly for 2 weeks, then every 3 months. Check folate levels before B12 replacement to avoid masking folate deficiency.
• Sickle cell disease (SCD): HbSS or HbSC. Presents with vaso-occlusive crises (bone pain, acute chest syndrome, priapism). Diagnosis: Hb electrophoresis shows HbS >50%. Management: analgesia (morphine), IV fluids, oxygen, antibiotics (if infection). Hydroxycarbamide (hydroxyurea) reduces crisis frequency. Vaccinate against pneumococcus, meningococcus, Haemophilus influenzae b. Avoid dehydration, hypoxia, acidosis.
• Disseminated intravascular coagulation (DIC): Consumptive coagulopathy from sepsis, trauma, malignancy (e.g., acute promyelocytic leukaemia). Labs: prolonged PT/APTT, low fibrinogen, elevated D-dimer, thrombocytopenia. Treatment: treat underlying cause. If bleeding: give cryoprecipitate (target fibrinogen >1.5 g/L), FFP, platelets (if <50 x10^9/L). Heparin only for thrombotic DIC (rare).
• Warfarin management and reversal: Target INR 2-3 for most indications (AF, DVT, PE). Reversal: if INR >5 with bleeding, give vitamin K 5 mg IV (slow) and prothrombin complex concentrate (PCC) 25-50 U/kg. For life-threatening bleeding (e.g., intracranial haemorrhage) regardless of INR, give PCC + IV vitamin K. Do not use FFP alone for urgent reversal.
• Acute leukaemia (AML vs ALL): Presents with pancytopenia (anaemia, thrombocytopenia, neutropenia) and blasts on blood film. AML: more common in adults, Auer rods on smear. ALL: more common in children, L1/L2 blasts. Urgent referral to haematology. Bone marrow biopsy with immunophenotyping for diagnosis. Start broad-spectrum antibiotics if febrile neutropenia (e.g., piperacillin-tazobactam).
• Hereditary haemochromatosis: Autosomal recessive (HFE gene C282Y mutation). Presents with fatigue, arthralgia, bronze skin, diabetes, cirrhosis. Labs: elevated ferritin (>300 ng/mL men, >200 ng/mL women), transferrin saturation >45%. Treatment: venesection (phlebotomy) weekly until ferritin <50 ng/mL, then maintenance every 2-4 months. Avoid vitamin C supplements and alcohol.
• Immune thrombocytopenic purpura (ITP): Isolated thrombocytopenia (<100 x10^9/L) with normal Hb and WCC. Petechiae, bruising. Diagnosis of exclusion. First-line: prednisolone 1 mg/kg/day for 2-4 weeks. If no response: IV immunoglobulin (IVIG) 1 g/kg. Second-line: rituximab, eltrombopag, or splenectomy. Avoid NSAIDs and intramuscular injections.

Common Traps in Haematology Questions

• Assuming microcytic anaemia is always iron deficiency — always check ferritin and consider thalassaemia trait (elevated HbA2) in ethnic groups.
• Giving folic acid alone in macrocytic anaemia without checking B12 — can precipitate subacute combined degeneration of the cord if B12 deficient.
• Using FFP as first-line for warfarin reversal in life-threatening bleeding — PCC is preferred as it is more rapid and complete.
• Treating sickle cell vaso-occlusive crisis with simple blood transfusion — this can increase viscosity; exchange transfusion is indicated only for acute chest syndrome or stroke.
• Forgetting to check coagulation screen before lumbar puncture or central line insertion — must have platelets >50 x10^9/L and INR <1.4.
• Confusing haemophilia A (factor VIII deficiency) with von Willebrand disease — vWD has prolonged APTT and bleeding time, but also low vWF antigen and ristocetin cofactor activity.

How to Revise Haematology for the PLAB 1

Prioritise anaemia classification (microcytic, normocytic, macrocytic) with specific cut-offs and causes. Focus on interpreting FBC and coagulation results in clinical vignettes — e.g., a patient with fatigue, pallor, and low MCV/high RDW (IDA) versus normal RDW (thalassaemia). Practise anticoagulation scenarios: bridging for surgery, reversal, and DOAC monitoring (no routine testing needed). Know the NICE guidelines for management of ITP, SCD, and haemochromatosis. Questions often frame a case with a blood film description (e.g., 'blasts seen', 'spherocytes', 'bite cells') and ask for the most likely diagnosis or next step. Revise transfusion reactions (acute haemolytic, febrile, allergic, TRALI) and correct product (e.g., irradiated blood for at-risk patients). Finally, be comfortable with DIC and thrombophilia workup — but avoid over-testing for thrombophilia during acute thrombosis.

Practise it: MedLumen has 50 Haematology questions for the PLAB 1, each with a full explanation and references.