Haematology
Core concepts
Classify anaemia by mean corpuscular volume. Microcytic: iron deficiency (low ferritin, low transferrin saturation), thalassaemia (normal or high ferritin, target cells, family history), anaemia of chronic disease (low iron, low TIBC, high ferritin). Normocytic: acute blood loss, CKD, haemolysis, marrow infiltration. Macrocytic: B12/folate deficiency, alcohol, hypothyroidism, myelodysplasia, drugs. Haemolysis: raised reticulocytes, raised LDH and unconjugated bilirubin, low haptoglobin; direct Coombs for immune causes. Sickle cell disease: vaso-occlusive crises, acute chest syndrome, sequestration, aplastic crisis with parvovirus, hydroxycarbamide. Leukaemia: acute myeloid (Auer rods, older adults), acute lymphoblastic (children, CNS prophylaxis), chronic myeloid (Philadelphia chromosome, imatinib), chronic lymphocytic (smudge cells, watch and wait). Lymphoma: Hodgkin (Reed-Sternberg cells, B symptoms, mediastinal mass) versus non-Hodgkin. Myeloma: CRAB features, paraprotein, marrow plasma cells; avoid NSAIDs. Thrombocytopenia: ITP (isolated, no splenomegaly), TTP (pentad, schistocytes, normal PT and APTT, urgent plasma exchange), HIT (heparin, thrombosis, stop heparin). Coagulation: haemophilia A (prolonged APTT), von Willebrand disease (prolonged bleeding time and APTT), DIC (prolonged PT and APTT, low fibrinogen, high D-dimer).
Traps
Giving platelets in TTP or HIT. Treating iron deficiency without finding the source. Missing B12 deficiency in vegans or metformin users. Forgetting ferritin is an acute phase reactant.
Rule of thumb
In microcytic anaemia a low ferritin confirms iron deficiency, but a normal or high ferritin does not exclude it - inflammation raises ferritin, so check transferrin saturation.