A 22-year-old woman is found to have hypochromic microcytic anaemia (Hb 8.2 g/dL, MCV 62 fL). Serum ferritin is 85 ng/mL, serum iron 90 µg/dL, TIBC 280 µg/dL. Red cell distribution width (RDW) is 13.2% (normal). Peripheral smear shows target cells and basophilic stippling. HPLC (haemoglobin electrophoresis) shows HbA 93%, HbA2 2.1%, HbF 1.4%. What is the most likely diagnosis?
- A Beta thalassaemia minor — HbA2 should be > 3.5%
- B Iron deficiency anaemia — low ferritin and low MCV
- C Alpha thalassaemia trait (alpha thalassaemia minor) — low HbA2, normal iron stores ✓
- D Anaemia of chronic disease — elevated ferritin with low TIBC expected
Explanation
Alpha thalassaemia trait (alpha thalassaemia minor, loss of 2 of 4 alpha-globin genes) is characterised by mild microcytic hypochromic anaemia with normal to low-normal iron stores, a normal HbA2 level (unlike beta thalassaemia minor where HbA2 > 3.5%), and normal HbF. The diagnosis is one of exclusion after ruling out iron deficiency (ferritin here is normal at 85 ng/mL) and beta thalassaemia (HbA2 is 2.1%, normal range 2.0–3.5%). Basophilic stippling and target cells are seen in both alpha and beta thalassaemia. Confirmation requires alpha-globin gene analysis (PCR). Low RDW (normal in this case) favours thalassaemia trait over iron deficiency (where RDW is typically elevated reflecting anisocytosis).
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.