Mentzer index
MCV ÷ red cell count — iron deficiency vs thalassaemia trait in microcytosis
Sources last checked: 2026-11-03
Mentzer index
MCV ÷ red cell count — iron deficiency vs thalassaemia trait in microcytosis
A screening index, not a diagnosis. Combined iron deficiency and thalassaemia trait, α-thalassaemia, pregnancy, children and anaemia of chronic disease all blur the cut-off; it is only meaningful in microcytosis.
Interpretation
| < 13 — favours thalassaemia trait | Mentzer (1973): an index below 13 points towards thalassaemia trait, in which the red cell count is relatively preserved despite small cells. Confirmation needs haemoglobin analysis (HbA₂/HbF) and iron studies. |
|---|---|
| ≥ 13 — favours iron deficiency | Mentzer (1973): an index above 13 points towards iron deficiency. Validation studies show substantial overlap, so ferritin and, where appropriate, haemoglobin analysis still decide. |
What is the Mentzer index?
The Mentzer index divides the mean corpuscular volume by the red cell count. William Mentzer proposed it in a 1973 letter to the Lancet as a quick way to separate iron deficiency from thalassaemia trait in microcytic anaemia: in thalassaemia trait the red cell count is relatively high, so the index is low.
When to use it
- Microcytosis (low MCV) on a routine blood count, as a first orientation
- Deciding which confirmatory test to request first (ferritin vs haemoglobin analysis)
- Teaching the red cell indices in microcytic anaemia
When not to use it
- Normocytic or macrocytic anaemia
- As a substitute for ferritin or haemoglobin electrophoresis/HPLC
- When iron deficiency and thalassaemia trait may coexist, which is common in high-prevalence populations
How it is calculated
Mentzer index = MCV (fL) / RBC (× 10¹²/L)
Clinical pearls and limitations
- A screening index, not a diagnosis. Combined iron deficiency and thalassaemia trait, α-thalassaemia, pregnancy, children and anaemia of chronic disease all blur the cut-off; it is only meaningful in microcytosis.
- Below 13 favours thalassaemia trait, above 13 iron deficiency; values close to 13 are uninformative.
- Iron deficiency can lower HbA₂ and mask β-thalassaemia trait — repeat haemoglobin analysis after iron repletion if suspicion remains.
- Validation studies show variable performance, especially in children and in α-thalassaemia.
- Relevant for premarital and antenatal screening programmes in Turkey and in Mediterranean-origin populations in Germany and Austria.
Frequently asked questions
How is the Mentzer index calculated?
MCV in fL divided by the red cell count in 10¹²/L (the same number as 10⁶/µL).
What does a Mentzer index below 13 mean?
It favours thalassaemia trait over iron deficiency; confirmation needs haemoglobin analysis and iron studies.
Is the Mentzer index reliable?
It is a quick screen with modest accuracy; studies report sensitivities and specificities ranging widely, so it does not replace ferritin and HbA₂.
Evidence and guidelines
- Primary source: Mentzer WC Jr. Differentiation of iron deficiency from thalassaemia trait. Lancet 1973;1(7808):882.
- AlQarni AM et al. Diagnostic test performance of the Mentzer index in evaluating Saudi children with microcytosis. Front Med 2024;11:1361805 (sensitivity 74 %, specificity 63 % for β-thalassaemia trait).
Have a follow-up question?
Medelix answers clinical questions from current guidelines and studies — every statement with its source.
Related calculators
Embed this calculatorFree to use on your website, intranet or teaching page. Copy the code below.
<iframe src="https://medelix.ai/en/embed/mentzer-index" title="Mentzer index – Medelix" width="100%" height="620" style="border:0;max-width:720px" loading="lazy"></iframe>
<p><a href="https://medelix.ai/en/calculators/mentzer-index">Mentzer index calculator by Medelix</a></p>For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.