Last updated October 4, 2026 · Report an error
Mentzer Index (MI) = MCV / RBC count, a standard published screening ratio (Mentzer WC Jr, "Differentiation of iron deficiency from thalassaemia trait", Lancet 1973;1(7808):882) commonly cited as a quick reference to help distinguish iron-deficiency anemia (MI typically above ~13) from thalassemia trait (MI typically below ~13) in a microcytic anemia workup. Pure arithmetic on given lab values — a screening reference ratio only, not a definitive diagnostic test. For general reference and educational purposes only — not a medical diagnosis. Consult a doctor for actual anemia workup and diagnosis.
How it works
Enter MCV and RBC count. The tool divides MCV by RBC count and compares the result to the commonly cited threshold of 13.
- Enter mCV (fL).
- Enter rBC count (x10^6/uL).
- Click Calculate to see your results.
Examples
MCV 70, RBC 5.5
MI = 70 / 5.5 = 12.7 — below 13, commonly cited as suggestive of thalassemia trait.
MCV 70, RBC 3.5
MI = 70 / 3.5 = 20 — above 13, commonly cited as suggestive of iron-deficiency anemia.
Who should use it
- Microcytic anemia workup education.
- Hematology reference.
Industry applications
- Hematology reference
- Clinical education
Advantages
- Simple, widely-cited screening formula.
- Long track record in clinical teaching since 1973.
Limitations
- Screening reference only — not a definitive diagnostic test.
- Can be misleading in mixed anemias or with certain comorbidities.
Common mistakes to avoid
- Treating the Mentzer Index as a definitive diagnosis rather than a screening reference ratio.
Best practices
- Use this alongside other iron studies and a doctor's clinical evaluation when investigating a microcytic anemia.
Tips
- If the Mentzer Index is borderline near 13, further testing (iron studies, hemoglobin electrophoresis) is typically needed rather than relying on this ratio alone.