Mentzer Index (Microcytic Anemia Screen)
Compute the Mentzer index (MCV in fL divided by RBC count in millions/microL) as a quick screen in microcytic anemia.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- MCV
- 65 fL
- RBC count
- 6.0 x10^12/L
Result: Index ~10.8 - favors beta-thalassemia trait.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- <13
- Favors beta-thalassemia trait.
- ~13
- Indeterminate.
- >13
- Favors iron-deficiency anemia.
What you enter
- MCV
- RBC count
What this is
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.
How this is calculated
Mentzer WC. Lancet 1973;1:882. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.
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