Mentzer index calculator and normal range
Short answer: The Mentzer index has no normal range in the usual sense. It is a cut-off of 13, used when red cells are small (MCV below 80 fL): a result below 13 suggests thalassaemia trait, and 13 or above suggests iron deficiency. It is a first pointer only. Ferritin and haemoglobin electrophoresis give the answer.
Free calculator
Mentzer index calculator
Mentzer index = MCV ÷ red cell count
Source: Mentzer WC. Differentiation of iron deficiency from thalassaemia trait. Lancet 1973;1(7808):882.
In fL, from your full blood count
In millions per µL, the same number as ×10¹²/L. For example 4.8
Your result
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A pointer, not a diagnosis. Talk to a doctor about your result, and sooner if you feel unwell.
Helps distinguish iron-deficiency (>13) from thalassaemia trait (<13).
How to read it
Adult reference range.
- Thalassaemia trait likely< 13 index
- Iron deficiency likely≥ 13 index
What it measures
MCV divided by red cell count, used to tell iron deficiency from thalassaemia trait when the cells are small. Below thirteen points towards thalassaemia, above it towards iron.
What moves it
A calculation used to help distinguish iron deficiency from thalassaemia trait when red cells are small. A screening pointer, not a diagnosis.
What to do next
A screening pointer, not a diagnosis. Confirm with ferritin and, where it matters, haemoglobin electrophoresis.
How fast it responds
It follows the underlying cause.
Also reported as: mentzer
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Common questions
- What is the normal range for the Mentzer index?
- There is no normal range in the usual sense. The Mentzer index is a cut-off of 13, used only when red cells are small (MCV below 80 fL). Below 13 suggests thalassaemia trait, 13 or above suggests iron deficiency. With a normal MCV the number means little.
- How do you calculate the Mentzer index?
- Divide the MCV (in fL) by the red blood cell count (in millions per µL). For example, an MCV of 66 fL with a red cell count of 5.5 gives 66 ÷ 5.5 = 12.
- What does a Mentzer index below 13 mean?
- When red cells are small, a result below 13 points towards thalassaemia trait: the body makes a normal or high number of red cells, but each one is small. It is a screening pointer, not a diagnosis. Haemoglobin electrophoresis or an HbA2 test confirms it.
- What does a Mentzer index above 13 mean?
- Above 13 points towards iron deficiency: fewer red cells, and small ones. A ferritin test confirms it. If your MCV is normal, the index does not apply.
- How reliable is the Mentzer index?
- It is a quick first pointer, not a verdict. It is wrong more often when iron deficiency and thalassaemia trait occur together, in children and in pregnancy. Use it to decide what to test next, and talk to a doctor about the result.
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Reference ranges are general-population guidance compiled from common clinical laboratories, not a diagnosis. Lab-to-lab ranges differ. Always read your results with your doctor.