A 35-year-old woman has Hb 8.8 g/dL, MCV 66 fL, RBC count 5.8 × 10¹²/L, serum iron and ferritin normal, and HbA2 5.2% on HPLC. Her Mentzer index (MCV/RBC count) is 11.4. Which statement is correct?
- A The elevated Mentzer index >13 supports beta-thalassemia trait
- B The Mentzer index is not useful here since RBC count is normal
- C The Mentzer index <13 favors beta-thalassemia trait over iron deficiency ✓
- D A Mentzer index <13 indicates iron deficiency anemia requiring iron therapy
Correct answer: C. The Mentzer index <13 favors beta-thalassemia trait over iron deficiency
Explanation
Mentzer index <13 favors thalassemia trait while >13 favors iron deficiency. In thalassemia trait, the RBC count is relatively high for the degree of anemia (ineffective erythropoiesis is compensated by increased RBC production), keeping the ratio low. In iron deficiency, RBC count is disproportionately low, giving a higher ratio. Normal iron studies and elevated HbA2 confirm beta-thalassemia trait.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.