Mentzer Index Calculator (Thalassaemia vs Iron Deficiency)
The Mentzer index divides the mean corpuscular volume (MCV, fL) by the red-cell count (RBC, ×10¹²/L) to help distinguish beta-thalassaemia trait from iron-deficiency anaemia in a microcytic picture. A value under 13 suggests thalassaemia trait, and over 13 suggests iron deficiency.
Quick answer
The Mentzer index divides the mean corpuscular volume (MCV, in fL) by the red-cell count (RBC, in ×10¹²/L) to help separate beta-thalassaemia trait from iron-deficiency anaemia in a microcytic picture. An index under 13 suggests thalassaemia trait, over 13 suggests iron deficiency, and exactly 13 is indeterminate.
Full blood count values
Use the MCV and red-cell count from the same full blood count, in a microcytic anaemia.
How to use the Mentzer Index calculator
- 1Read the values from the full blood count. Take the MCV (fL) and the RBC count (×10¹²/L) from the same full blood count.
- 2Enter MCV and RBC. Enter both values into the tool.
- 3Read the index and its hint. The tool divides MCV by RBC and shows the index with its conventional interpretation. It is a pointer, not a diagnosis — confirmation needs further tests interpreted by a clinician.
Medical disclaimer: This is general health information, not medical advice. It does not diagnose or treat any condition, and the results are estimates based on public reference formulas. Always consult a qualified doctor about your individual health. If you think you may have a medical emergency, contact your local emergency services immediately.
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Book a consultationFrequently asked questions
How does the Mentzer index distinguish thalassaemia from iron deficiency?⌄
In beta-thalassaemia trait the red-cell count is typically preserved or raised despite a low MCV, giving a low index (under 13). In iron-deficiency anaemia the red-cell count falls, giving a higher index (over 13). It is a screening pointer only.
Is the Mentzer index definitive?⌄
No. It is a quick discriminator for microcytic anaemia but it is not diagnostic. Confirmation requires iron studies and haemoglobin electrophoresis (or HPLC), interpreted together by a clinician.
When is the index unhelpful?⌄
It is less reliable when iron deficiency and thalassaemia trait coexist, or in other causes of microcytosis such as anaemia of chronic disease. It should be read alongside the rest of the blood picture.
Is my data stored?⌄
No. The calculator runs entirely in your browser; nothing you enter is sent to a server.
Sources & validation
This calculator reproduces the published Mentzer Index score, validated for discriminating beta-thalassaemia trait from iron-deficiency anaemia.
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