A 24-year-old woman with menorrhagia has Hb 10.5 g/dL, MCV 66 fL, RDW 18%, and RBC count 4.1 million/uL. To distinguish iron deficiency from beta-thalassemia trait without waiting for electrophoresis, which derived value supports iron deficiency?

• A Serum iron above 100 mcg/dL
• B Mentzer index (MCV/RBC) of 11.3
• C Normal RDW with high RBC count
• D Mentzer index (MCV/RBC) of 16.1 ✓

Explanation

The Mentzer index divides MCV by RBC count. D value greater than 13 favors iron deficiency, where fewer, smaller red cells are produced, while a value less than 13 favors beta-thalassemia trait, where RBC counts are characteristically high relative to the degree of anemia. The elevated RDW also supports iron deficiency, since anisocytosis increases, whereas thalassemia trait typically shows a uniform microcytosis with near-normal RDW.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.