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For healthcare professionals

Mentzer Index

The Mentzer index helps tell beta-thalassemia trait from iron deficiency anemia in a person with small red blood cells (microcytic anemia). It divides the mean corpuscular volume (MCV) by the red blood cell count. Mentzer described it in 1973. This tool is written for clinicians and is not a diagnosis.

Last reviewed: By the uncovermyrisk.com editorial team Educational only, not medical advice.

Chest pain, severe shortness of breath or fainting: call 911 now.General safety advice (not part of the published index). The index is for blood test results already in hand.

Blood count

From a complete blood count. Nothing you enter leaves this page.

Result appears here

What you will see

The index, the working, and which condition the published cut-off points to.

Educational only, not medical advice. Not a diagnosis. Confirmation needs further blood tests.

Source

Mentzer WC, Lancet 1973. The formula, units and cut-off are taken from an open-access (CC BY) study, Althumairi A and colleagues, Frontiers in Medicine 2024; screening results in infants from an open-access (CC BY) study, Alkamali A and colleagues, Cureus 2024. The tests check the formula, the cut-off and the input ranges.

Validated in

People with microcytic anemia. Althumairi 2024 studied 434 children aged 16 or younger with MCV under 80 fL; Alkamali 2024 studied infants at first-year screening in primary care.

Limits

In 434 Saudi children, sensitivity was 74% and specificity 63% for beta-thalassemia trait, and the authors judged the index not highly reliable; it performs poorly for alpha-thalassemia and should not be used as a standalone diagnostic tool (Althumairi 2024). Children with both conditions at once were excluded from that study. Althumairi 2024 groups an index of exactly 13 with iron deficiency, while Alkamali 2024 prints only 'under 13' and 'over 13'; this page follows Althumairi 2024.

Formula

Mentzer index = MCV (fL) / red blood cell count (millions per microliter) (Althumairi 2024).

An index under 13 suggests thalassemia trait, and an index of 13 or more suggests iron deficiency anemia (Althumairi 2024). The index was first described by Mentzer (Mentzer 1973).

Worked example: an MCV of 70 fL and a red cell count of 4.0 million per microliter give 70 / 4.0 = 17.5, which suggests iron deficiency anemia.

What the studies found

Earlier studies reported sensitivity and specificity as high as 98.7% and 82.3%, but in 434 children with microcytosis in Saudi Arabia the index showed 74% sensitivity and 63% specificity for beta-thalassemia trait, with a negative predictive value of 98% (Althumairi 2024).

In 75 infants with low hemoglobin at first-year screening in Dubai, the reported sensitivity was 99% and specificity 54.5%. The diagnosis was confirmed with serum ferritin for iron deficiency and hemoglobin electrophoresis for thalassemia (Alkamali 2024).

Related calculators

For a low white cell count, see the absolute neutrophil count calculator. To check whether the marrow is keeping up with an anemia, see the reticulocyte production index calculator. For iron deficiency screening in pregnancy, see the iron deficiency in pregnancy check. Lead poisoning was an exclusion in the Althumairi study as a separate blood condition (Althumairi 2024); for lead testing in children, see the blood lead test check. Other bedside scores are listed under For healthcare professionals.

Sources

  1. Althumairi A, AlQarni AM, Alkaltham NK, et al. Diagnostic test performance of the Mentzer index in evaluating Saudi children with microcytosis. Front Med (Lausanne). 2024;11:1361805. doi:10.3389/fmed.2024.1361805. PMID 39135717. Open access (CC BY). Introduction (formula, earlier results), Methods (units, groups under 13 and 13 or more, exclusions), Results and Discussion (sensitivity, specificity, alpha-thalassemia, limits). pmc.ncbi.nlm.nih.gov/articles/PMC11317290/
  2. Alkamali A, Alshafiei LS, AlJasmi M, et al. Evaluating the Mentzer Index for Screening of Iron Deficiency Anemia and Beta Thalassemia Among Infants Visiting Primary Healthcare Centers in Dubai. Cureus. 2024;16(8):e66286. doi:10.7759/cureus.66286. PMID 39238747. Open access (CC BY). Methods (cut-off, reference tests) and Results (75 infants, sensitivity 99%, specificity 54.5%). pmc.ncbi.nlm.nih.gov/articles/PMC11375987/
  3. Mentzer WC. Differentiation of iron deficiency from thalassaemia trait. Lancet. 1973;1(7808):882. doi:10.1016/s0140-6736(73)91446-3. PMID 4123424. pubmed.ncbi.nlm.nih.gov/4123424/

Written and maintained by the uncovermyrisk.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-11-02. Spotted an error? See About.