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Mentzer Index (Thalassemia Trait vs Iron Deficiency)

Mentzer index = MCV (fL) ÷ RBC count (×10¹²/L). In microcytic anaemia, <13 suggests thalassaemia trait and >13 suggests iron deficiency.

  • MCV
  • Red cell count (×10¹²/L or ×10⁶/µL)
—

Interpretation

ResultMeaning
< 13Thalassaemia trait more likely
> 13Iron deficiency more likely

Formula

Mentzer index = MCV (fL) ÷ RBC (×10¹²/L, = millions/µL)

Clinical pearls

  • A screening heuristic only: confirm with ferritin and haemoglobin electrophoresis (HbA₂ for β-thal trait); coexisting iron deficiency can mask β-thal trait.
  • Less reliable in children, pregnancy and anaemia of chronic disease.

Examples

mentzer index mcv 65 rbc 5.8thal trait or iron deficiency: MCV 70, RBC 3.5

FAQ

What Mentzer index suggests thalassaemia?

Below 13: the red cell count is high relative to cell size, typical of thalassaemia trait.

Can the Mentzer index diagnose thalassaemia?

No. It only suggests which test to prioritise; diagnosis needs iron studies and haemoglobin electrophoresis or genetic testing.

Evidence

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

Hematology & Oncology · Reviewed 2026-10-14 · Methodology