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Mentzer index

Distinguishes beta-thalassemia trait from iron deficiency anemia using routine CBC indices.

Mentzer index
Mean corpuscular volume (MCV)
fL
Red blood cell count
x10^6/uL
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When to use

  • Rapidly differentiating thalassemia trait from iron deficiency anemia in a patient with microcytic anemia, pending iron studies/hemoglobin electrophoresis.

Formula

Mentzer index = MCV (fL) / RBC count (millions/uL). Index <13 favors thalassemia trait; >13 favors iron deficiency anemia.

Pearls and pitfalls

  • A screening aid only; confirm with iron studies and/or hemoglobin electrophoresis.
  • Least reliable when both conditions coexist or in the setting of recent transfusion.

References

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