Mentzer Index (microcytic anemia)

About this calculator

The Mentzer index helps differentiate microcytic anemia: beta-thalassemia (trait/minor) vs iron deficiency anemia. Proposed by Mentzer (Lancet, 1973). Formula: index = MCV (fL) / RBC count (×10¹²/L). Used only when MCV <80 fL. Interpretation. <13 – thalassemia more likely (trait/minor). 13-13.5 – indeterminate, repeat or perform hemoglobin electrophoresis. >13 – iron deficiency more likely; check ferritin, transferrin saturation, TIBC. Clinical rationale. In thalassemia the marrow compensates anemia with high RBC count and small MCV – index is lower. In iron deficiency the marrow cannot produce enough RBC, count drops proportionally to MCV – index is higher. Additional tests. Hemoglobin electrophoresis: HbA2 >3.5% – beta-thalassemia trait (diagnostic). Ferritin: <30 ng/mL – iron deficiency. Combinations are possible (dual etiology) – then both markers are intermediate. Children of Hispanic, Mediterranean, Asian, Middle Eastern descent have particularly common thalassemia as cause of microcytosis. Limitations. Fails when thalassemia and iron deficiency coexist – some patients fall in the indeterminate zone. Does not separate alpha-thalassemia and beta-thalassemia. Does not address anemia of chronic disease (ACD), which can be normocytic or microcytic with overlapping indices. In neonates and pregnancy physiologic MCV changes distort the calculation.

Source

Mentzer WC. Differentiation of iron deficiency from thalassaemia trait. Lancet. 1973;1(7808):882.

Formula version: mentzer-1973-v1