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HematologyMentzer Index

Mentzer Index Calculator

Calculate the Mentzer Index from same-CBC MCV and RBC count after microcytosis has been identified.

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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.

fL

Enter the exact ordinary decimal printed on the CBC, without spaces, signs, scientific notation, or units.

selected below

Enter the exact numeric RBC value from the same CBC as the MCV.

These units have the same numeric value. The selection records how the laboratory reported the count; it does not convert it.

Use MCV and RBC count from the same CBC. The Mentzer Index was developed as a screening ratio in a microcytosis or microcytic-anemia context. QuickMedCalc does not verify report identity or determine whether microcytosis is present; use the applicable laboratory and clinical reference context.

Mentzer Index result will appear here

Enter MCV and RBC count from the same CBC after microcytosis has been identified. This historical screening ratio does not diagnose iron deficiency or thalassemia.

About

The Mentzer Index divides mean corpuscular volume by red blood cell count. It is a historical screening ratio used after microcytosis has already been identified, not a diagnosis, exclusion test, or treatment rule. [1, 2]

Formula

Mentzer Index = MCV (fL) ÷ RBC count (million/µL or ×10¹²/L). [1]
1 million/µL = 1 ×10¹²/L numerically; the selected unit preserves the source-report label rather than changing the number.
Worked examples: 65 ÷ 5 = 13; 72 ÷ 5.5 ≈ 13.09. Both are generated by the frozen runtime and formatter.

Interpretation

Historical value 13 — static screening context

Historical relationship
Below 13
Original association
Historically associated with a thalassemia-trait pattern
Historical relationship
Exactly 13
Original association
Historical dividing boundary; no diagnosis is assigned
Historical relationship
Above 13
Original association
Historically associated with an iron-deficiency pattern

No row is selected from a submitted result. The value 13 is neither a universal cutoff nor a normal range. [1, 2]

Is 13 a universal Mentzer Index cutoff?

No. Thirteen is the historical teaching boundary for the original screening relationship. Studies use different populations, reference tests, prevalence, and sometimes different empirical cutoffs. A 2026 pediatric study of 550 analyzed children, for example, derived 11.97 in its own cohort rather than validating 13 as universal. [1, 4]

How reliable is the Mentzer Index?

A 2015 meta-analysis of 99 articles found no discriminant index with perfect sensitivity and specificity, inconsistent ranking across studies, and generally better performance in adults than children. In one 2024 Saudi cohort of 434 children with microcytosis, Mentzer sensitivity and specificity were 74% and 63% for β-thalassemia trait and 61% and 38% for iron deficiency anemia. These are population results, not an individual probability. [2, 3]

Mentzer Index versus iron studies

The ratio uses only two CBC measurements. It does not measure iron stores. Ferritin and other iron markers must be interpreted with the clinical and laboratory context, including inflammation; the Mentzer result cannot determine whether iron or another treatment is appropriate. [6]

Mentzer Index versus thalassemia testing

A ratio cannot diagnose or exclude beta-thalassemia trait, alpha-thalassemia, or another hemoglobinopathy. Screening and diagnosis can require red-cell indices and morphology, hemoglobin fraction separation and quantitation, family information, and genetic testing in selected cases. [5]

Important limits

Iron deficiency and thalassemia trait can coexist, and other causes of microcytosis are outside this two-pattern historical screen. Age, pregnancy, population, recent transfusion, specimen quality, analyzer methods, and the applicable laboratory interval can change the meaning of the source CBC. This calculator performs arithmetic only; it does not diagnose, exclude, recommend treatment, or decide whether testing is needed. [2, 5, 6]

References

  1. 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.
  2. 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.
  3. 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.
  4. Okay ZU, Okay B. Diagnostic accuracy of hematological indices and logistic regression for β-thalassemia carrier screening in children. Medicine (Baltimore). 2026;105(10):e47953. PMID 41790707. PMCID PMC12975230. DOI 10.1097/MD.0000000000047953.
  5. 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.
  6. 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.

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Disclaimer

Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.