Haematology
Practice questions with explanations

C. Spontaneous bleeding, petechiae, or a head injury, since severe thrombocytopenia risks intracranial haemorrhage

Bleeding risk rises steeply below a platelet count of about 20, and spontaneous mucosal bleeding or petechiae indicate significant thrombocytopenia. Patients are advised to avoid NSAIDs, aspirin, intramuscular injections, contact sport and razors, and to report bleeding promptly. Platelet transfusion thresholds depend on the clinical situation.

B. Microcytic hypochromic red cells with low ferritin and raised total iron binding capacity

Iron deficiency reduces haemoglobin synthesis, so cells are small and pale, and depleted stores show as low ferritin with the liver making more transferrin, hence a high binding capacity. Anaemia of chronic disease can also be microcytic but shows normal or raised ferritin with low binding capacity, since ferritin is an acute phase reactant. Macrocytosis points to B12 or folate deficiency, alcohol, hypothyroidism or drugs.

B. Oxidant drugs such as primaquine, dapsone, nitrofurantoin and sulfonamides

Glucose-6-phosphate dehydrogenase generates the NADPH that keeps glutathione reduced, protecting red cells from oxidative stress. Without it, oxidant drugs, fava beans and infection precipitate haemolysis with Heinz bodies and bite cells. The deficiency is X-linked and common in people of Mediterranean, African, Middle Eastern and South-East Asian ancestry, so screening before primaquine or dapsone is standard.