Mentzer Index Calculator for Microcytosis
Calculate the historical Mentzer Index from same-CBC MCV and RBC count as a non-diagnostic screening aid for microcytosis.
Content updated: View sources
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Formula and medical content are based on the references listed on this page. See sources, About, and Sources and Review Process.
About
Formula
Interpretation
Historical screening context — not calculated
| Historical index relationship | Original screening association |
|---|---|
| Below 13 | Historically associated with a thalassemia-trait pattern |
| Above 13 | Historically associated with an iron-deficiency pattern |
| Exactly 13 | Historical dividing boundary |
The table is static historical context. No row is selected from a result. Published performance varies by population, age, case definition, and prevalence, and no discriminant index is perfectly sensitive or specific.
Iron deficiency and thalassemia trait can coexist. Evaluation may require ferritin and other iron markers interpreted with infection, inflammation, and the clinical context. Beta-thalassemia carrier detection uses red-cell indices and morphology together with hemoglobin-fraction separation and measurement; alpha-thalassemia may require molecular confirmation. One calculated ratio cannot perform any of those diagnostic steps.
References
- Mentzer WC Jr. Differentiation of iron deficiency from thalassaemia trait. Lancet. 1973;1(7808):882. PMID 4123424. DOI 10.1016/S0140-6736(73)91446-3.
- Hoffmann JJML, Urrechaga E, Aguirre U. Discriminant indices for distinguishing thalassemia and iron deficiency in patients with microcytic anemia: a meta-analysis. Clin Chem Lab Med. 2015;53(12):1883–1894. PMID 26536581. DOI 10.1515/cclm-2015-0179.
- Vehapoglu A, et al. Hematological indices for differential diagnosis of beta thalassemia trait and iron deficiency anemia. Anemia. 2014;2014:576738. PMID 24818016. DOI 10.1155/2014/576738.
- Althumairi A, et al. Diagnostic test performance of the Mentzer index in evaluating Saudi children with microcytosis. Front Med (Lausanne). 2024;11:1361805. PMID 39135717. DOI 10.3389/fmed.2024.1361805.
- Old J, Harteveld CL, Traeger-Synodinos J, et al. Prevention of Thalassaemias and Other Haemoglobin Disorders: Volume 2, Laboratory Protocols. 2nd ed. Thalassaemia International Federation; 2012.
- Bain BJ, et al. Significant haemoglobinopathies: a guideline for screening and diagnosis. Br J Haematol. 2023;201(6):1047–1065. PMID 37271570. DOI 10.1111/bjh.18794.
- Fletcher A, Forbes A, Svenson N, Thomas DW. Guideline for the laboratory diagnosis of iron deficiency in adults (excluding pregnancy) and children. Br J Haematol. 2022;196(3):523–529. PMID 34693519. DOI 10.1111/bjh.17900.
- World Health Organization. WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. 2020. ISBN 978-92-4-000012-4.
- Origa R. Beta-Thalassemia. GeneReviews. Updated 2025.
- Musallam KM, et al. TIF Guidelines for the Management of Transfusion-Dependent β-Thalassemia. HemaSphere. 2025;9(3):e70095. PMID 40045934. DOI 10.1002/hem3.70095.
- National Heart, Lung, and Blood Institute. Thalassemia diagnosis.
FAQ
It is the mean corpuscular volume in fL divided by the numeric red blood cell count reported in million/µL or the numerically equivalent ×10¹²/L.
The ratio combines two measurements. Using values from different samples can combine different physiologic and laboratory time points.
Select million/µL or ×10¹²/L exactly as printed on the report. These two units have the same numeric value, so the calculator records the label without changing the number.
The original screening convention associated values below 13 with a thalassemia-trait pattern and values above 13 with an iron-deficiency pattern. It is historical context, not a universal diagnostic cutoff.
Exactly 13 is the historical dividing boundary. This page does not convert it, or any other value, into a diagnosis or positive/negative result.
No. Iron deficiency must be assessed independently. Ferritin and other iron markers need interpretation with infection, inflammation, laboratory methods, symptoms, and the rest of the CBC; this page applies no universal ferritin cutoff.
No. Beta-thalassemia carrier detection uses red-cell indices and morphology with hemoglobin-fraction separation and measurement. Alpha-thalassemia may require molecular confirmation. The Mentzer Index performs none of those tests.
Yes. Coexistence can alter red-cell indices and make a simple binary screening ratio misleading.
No single performance estimate applies everywhere. Published sensitivity and specificity vary by age, population, prevalence, laboratory method, and study design.
Inflammation-related iron restriction, lead exposure, sideroblastic processes, and other causes are outside this two-pattern historical index.
No. Meta-analytic and validation evidence shows that discriminant indices are not perfectly sensitive or specific and are not definitive tests.
Recent transfusion, analyzer methods, specimen quality, and timing can alter the component measurements. Review the original laboratory report and clinical context.
Pregnancy can change anemia evaluation and iron requirements. This arithmetic page does not provide pregnancy-specific diagnosis or treatment guidance.
No. Empiric treatment from this ratio alone can miss another cause or coexistence. This page does not recommend iron, a dose, or any other therapy.
The calculation uses the exact submitted decimals. When the exact quotient needs more than two displayed decimal places, the page uses ≈ to show that only the display was rounded.
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Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.