A pregnant woman at 20 weeks has haemoglobin 7.8 g/dL. Peripheral smear shows microcytic hypochromic anaemia with target cells. Serum ferritin is 62 ng/mL (normal). Haemoglobin electrophoresis shows HbA2 5.8% and HbF 3.2%. The most likely diagnosis is:

• A Iron deficiency anaemia
• B HbE disease
• C Beta-thalassaemia trait ✓
• D Alpha-thalassaemia trait

Explanation

HbA2 >3.5% (here 5.8%) with elevated HbF and microcytic hypochromic anaemia with a normal serum ferritin is diagnostic of beta-thalassaemia trait. In iron deficiency, HbA2 may be falsely normal or low; ferritin would be low. HbE disease shows HbE on electrophoresis with HbA2 within normal range. Alpha-thalassaemia trait shows normal HbA2 and HbF (since alpha chains are needed for HbA2 and HbF synthesis, alpha deficiency reduces all fractions proportionally). Genetic counselling and partner testing are mandatory in this case.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.