Mentzer Index (Microcytic Anemia Screen)
Mentzer Index (Microcytic Anemia Screen) - a deterministic tool in Sophie Well's Clinical Scoring & Risk group.
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What this is
Compute the Mentzer index (MCV in fL divided by RBC count in millions/microL) as a quick screen in microcytic anemia. An index above 13 favors iron-deficiency anemia (where the red-cell count drops out of proportion to the microcytosis); an index below 13 favors beta-thalassemia trait (where the red-cell count is preserved or elevated despite a markedly low MCV). Sophie Well returns the index to one decimal and labels which side of the threshold it falls on.
When to use it
Use this as a first-pass orientation when you see a microcytic CBC and are deciding whether to send iron studies (favoring iron deficiency) or a hemoglobin electrophoresis (favoring thalassemia). It is a screening number, not a diagnosis - mixed pictures (iron deficiency superimposed on thalassemia trait, anemia of chronic disease) blur the threshold, and the index does not discriminate iron deficiency from anemia of chronic disease or sideroblastic anemia. Pair it with ferritin, transferrin saturation, RDW, and, when indicated, hemoglobin electrophoresis before settling on a diagnosis.
References
Mentzer WC. Lancet 1973;1:882.
Worked example: Index ~10.8 - favors beta-thalassemia trait.
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