A 27-year-old primigravida at 20 weeks has haemoglobin 10.2 g/dL, MCV 64 fL, RDW 13.5% (normal), serum ferritin 35 ng/mL, and red cell count 5.9 million/mm3. Her Mentzer index is 10.8. She has not responded fully to two months of oral iron. What is the next most appropriate investigation?

• A Repeat full blood count after another month of iron
• B Serum vitamin B12 and folate levels
• C Bone marrow aspiration
• D Haemoglobin electrophoresis or HPLC for HbA2 estimation ✓

Explanation

Low MCV with normal RDW, normal or high red cell count, borderline ferritin, Mentzer index below 13 and poor response to iron point to beta thalassaemia trait rather than isolated iron deficiency. Diagnosis is confirmed by HPLC or electrophoresis showing raised HbA2 above 3.5%. The tempting option, more iron, fails because iron stores are adequate and the microcytosis is genetic, not nutritional.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.