In thalassaemia trait the marrow makes many small red cells, so the count is normal or high; in iron deficiency it makes fewer cells. The index is a quick screen – iron studies and haemoglobin electrophoresis confirm the diagnosis.
How to use the Mentzer Index Calculator
- MCV
- Red blood cell count
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter MCV and red cell count.
Inputs explained
| Field | What to enter |
|---|---|
| MCV | In fL |
| Red blood cell count | In ×10¹²/L |
Example values
How the main result changes when MCV changes and everything else stays at the example values above:
| MCV (fL) | Mentzer index |
|---|---|
| 51 | 9.1 |
| 68 | 12.1 |
| 85 | 15.2 |
| 102 | 18.2 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Mentzer index = MCV (fL) ÷ RBC (×10¹²/L)
< 13: thalassaemia trait more likely · > 13: iron deficiency more likely
Worked example
Inputs — MCV: 68 fL; Red blood cell count: 5.6 ×10¹²/L.
Results — Mentzer index = 12.1; Suggests = Thalassaemia trait more likely.
Key terms
- Thalassaemia trait
- Carrier state of thalassaemia with mild microcytosis.
Frequently asked questions
How accurate is the Mentzer index?
Useful as a first screen, but it misclassifies some patients.
Can both conditions occur together?
Yes – iron deficiency can coexist with thalassaemia trait.
What confirms thalassaemia?
Haemoglobin electrophoresis or HPLC, and sometimes genetic testing.