Master Haematology
for MRCP Part 1

What the MRCP Part 1 Tests in Haematology

MRCP Part 1 Haematology tests the ability to diagnose and manage common haematological disorders based on clinical presentations, full blood count and film findings, coagulation profiles, and relevant immunophenotyping or genetic results. Candidates must know diagnostic criteria for conditions like polycythaemia vera, essential thrombocythaemia, and myelodysplastic syndromes; first-line therapies including anticoagulation choices (DOACs vs warfarin) and transfusion triggers; and interpretation of haematinics, haemoglobin electrophoresis, and direct antiglobulin test. Emphasis is on linking laboratory abnormalities to clinical scenarios, recognising haematological emergencies (e.g., DIC, hyperviscosity, tumour lysis syndrome), and applying BCSH or NICE guidelines for common conditions like iron deficiency anaemia, venous thromboembolism, and immune thrombocytopenia.

High-Yield Concepts

• Diagnostic criteria for polycythaemia vera (PV): Major criteria: Hb >165 g/L (men) or >160 g/L (women) OR Hct >0.49 (men) or >0.48 (women); JAK2 V617F mutation. Minor criterion: low serum erythropoietin. Diagnosis requires both major criteria, or first major plus minor. First-line: venesection to target Hct <0.45, plus low-dose aspirin if no contraindication.
• Management of immune thrombocytopenia (ITP): First-line: prednisolone 1 mg/kg/day for 2-4 weeks then taper, or IVIG 1 g/kg if bleeding/need for rapid rise. Second-line: thrombopoietin receptor agonists (eltrombopag, romiplostim) or rituximab. Splenectomy reserved for refractory cases. Platelet count target >20-30 x10⁹/L unless bleeding.
• Anticoagulation in venous thromboembolism (VTE): First-line: DOACs (apixaban, rivaroxaban) for initial and maintenance therapy, avoiding in severe renal impairment (CrCl <15 mL/min). Warfarin used for mechanical heart valves, antiphospholipid syndrome (target INR 2-3 or 3-4). Duration: provoked VTE 3 months; unprovoked VTE at least 3 months, consider extended therapy.
• Diagnosis and management of disseminated intravascular coagulation (DIC): Diagnosis: ISTH DIC score (platelets, PT, fibrinogen, D-dimer) >5 indicates overt DIC. Treatment: treat underlying cause; platelet transfusion if <50 x10⁹/L with bleeding; cryoprecipitate if fibrinogen <1.5 g/L; FFP if PT/APTT prolonged and bleeding. Avoid heparin unless overt thrombosis.
• Haemoglobin electrophoresis interpretation in thalassaemia: Beta thalassaemia major: HbF >90%, absent/minimal HbA. Beta thalassaemia trait: HbA2 >3.5% (usually 4-6%), HbF mildly raised. Alpha thalassaemia trait: normal HbA2, low MCV/MCH, no HbH on electrophoresis (confirmed by genetic testing). HbH disease: fast-moving HbH band, Hb Bart's in neonates.
• Transfusion thresholds and complications: Restrictive threshold: Hb <70 g/L in stable patients (80 g/L if cardiac disease). Massive transfusion protocol: 1:1:1 ratio of RBCs:FFP:platelets. Acute transfusion reaction: stop transfusion, check ABO compatibility, manage anaphylaxis with IM adrenaline. TRALI: acute hypoxaemia within 6 hours of transfusion, bilateral infiltrates, no cardiac cause.
• Myelodysplastic syndromes (MDS) risk stratification and treatment: IPSS-R uses cytopenias, marrow blasts, cytogenetics (e.g., -5/del5q, -7, complex). Low-risk: supportive care (growth factors, transfusions, lenalidomide for del5q). High-risk: hypomethylating agents (azacitidine) or allogeneic stem cell transplant. Iron chelation if >20 units transfused and ferritin >1000 ng/mL.
• Haemolytic anaemia workup: Raised LDH, unconjugated bilirubin, reticulocytosis, low haptoglobin. Direct antiglobulin test (DAT) positive: autoimmune haemolytic anaemia (warm AIHA: IgG, responds to steroids; cold AIHA: IgM, avoid cold, rituximab). DAT negative: consider hereditary spherocytosis (family history, osmotic fragility test), G6PD deficiency (X-linked, triggered by oxidants), or microangiopathic haemolytic anaemia (schistocytes, low platelets).

Common Traps in Haematology Questions

• Confusing iron deficiency anaemia (low ferritin, high TIBC) with anaemia of chronic disease (low ferritin only in severe cases, low TIBC, high hepcidin).
• Assuming a normal PT/APTT excludes all bleeding disorders: von Willebrand disease may have normal PT/APTT, requiring vWF antigen and activity assay.
• Giving vitamin K alone for warfarin reversal in major bleeding: must give prothrombin complex concentrate (PCC) 25-50 U/kg plus IV vitamin K 5-10 mg.
• Missing hyperviscosity syndrome in Waldenström's macroglobulinaemia: present with blurred vision, headache, epistaxis, and fundoscopy showing 'sausage-like' veins; treat with plasmapheresis.
• Forgetting that heparin-induced thrombocytopenia (HIT) requires stopping all heparin and starting a non-heparin anticoagulant (e.g., argatroban, danaparoid), not just monitoring platelets.
• Interpreting a positive D-dimer as diagnostic for VTE: D-dimer is non-specific, elevated in pregnancy, malignancy, and post-surgery; use Wells score to pre-test probability.

How to Revise Haematology for the MRCP Part 1

For MRCP Part 1 Haematology, prioritise memorising diagnostic criteria and first-line treatments for common conditions: PV, ET, ITP, VTE, and haemolytic anaemias. Focus on interpreting full blood count differentials, blood film descriptions, and coagulation profiles in clinical vignettes. Practise linking lab findings to specific disorders (e.g., microcytic hypochromic anaemia with raised HbA2 = beta thalassaemia trait). Be comfortable with transfusion triggers and complications, as well as the ISTH DIC score. Questions often present as 'which test confirms diagnosis?' or 'what is the next management step?'—avoid over-investigating when simple criteria suffice. Review BCSH guidelines for anticoagulation in special populations (cancer, pregnancy) and know the differences between warm and cold AIHA. Do not neglect haematological emergencies like DIC, hyperviscosity, and tumour lysis syndrome.

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