A 28-year-old woman from the Mediterranean has moderate anaemia (Hb 8.1 g/dL), target cells, microcytosis, splenomegaly, and Hb electrophoresis showing HbA 70%, HbA₂ 5.8%, HbF 3%. Which is the diagnosis and what does the elevated HbA₂ indicate?

• A HbE disease; HbA₂ elevation indicates β-chain structural variant
• B Beta-thalassaemia trait; HbA₂ >3.5% is the hallmark of β-thalassaemia minor ✓
• C Iron deficiency anaemia; HbA₂ elevation is reactive
• D Alpha-thalassaemia trait; confirmed by elevated HbA₂

Explanation

Beta-thalassaemia trait (β-thalassaemia minor) is characterised by HbA₂ >3.5% (normal <3.2%), which is the diagnostic hallmark. In β-thalassaemia trait, reduced β-globin synthesis causes relative excess of δ-chains, which combine with α-chains to form HbA₂ (α₂δ₂). HbF is mildly elevated (2-5%). Patients typically have mild microcytic anaemia (Hb 10-13 g/dL) with target cells and a disproportionately low MCV relative to anaemia severity (Mentzer index <13). Alpha-thalassaemia does NOT elevate HbA₂. Iron deficiency reduces HbA₂. This finding is critical for genetic counselling and prevention of thalassaemia major in offspring.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.