Anaemia Indices: The Evidence Behind the Calculator

A 22-year-old nursing student from Udupi has her blood tested before her wedding. Her haemoglobin is 10.4 g/dL, her mean corpuscular volume 64 fL and her red cell count 5.6 × 10¹²/L. She has been given iron twice before, and it made no difference. Her mother asks whether she simply needs a stronger tablet. This is an illustrative case, not a real patient.

The Anaemia Indices Calculator works out eight indices from the blood count, the reticulocyte production index and the WHO thresholds. It keeps every formula, every cut-off and every threshold. What it no longer carries is where each index came from, how they perform in Indian patients, and the figures for India as a whole. Those have moved here. By the end you will know why her red cell count is the most important number on her report.

1. Eight indices, one idea

In iron deficiency the marrow makes fewer red cells, and they are small. In beta-thalassaemia trait the marrow makes plenty of red cells, and each one is small. Every index asks the same question: how small are the cells, compared with how many there are? Here are the eight the tool computes, with the paper each comes from.

Work the Mentzer index for our student. Her MCV of 64 divided by her red cell count of 5.6 is about 11.4. That is below 13, which favours the trait. Her count is high while her cells are small. Iron does not do that.

2. Cut-offs from Europe, patients from India

“If the index says trait, can I tell her she has it?” Not on the index alone. The largest analysis of these indices, 99 studies and 135,409 results, found performance markedly worse in South-East Asian populations than in European ones, a pooled diagnostic odds ratio of 9.3 against 53.1. A diagnostic odds ratio is one number for how well a test separates two conditions; the higher it is, the better. An odds ratio almost six times higher in Europe than here describes a test to use with care.

Kumar and colleagues at Manipal tested the classical indices against HPLC-confirmed cases, and found that every published cut-off did better once it was re-derived locally. Here is their table whole.

The tool prints both cut-offs wherever a local one exists. When the two disagree on a patient, that is the honest state of the evidence, not a fault in the tool.

3. The patient who has both

“Could she have the trait and be short of iron as well?” She could, and in India this matters more than anywhere. In a Delhi series of 463 people with beta-thalassaemia trait, 27.2 per cent also had iron deficiency, with haemoglobin, mean corpuscular volume and mean corpuscular haemoglobin all significantly lower than in iron-replete carriers. Haemoglobin A₂ stayed elevated in all but one of the iron-deficient carriers in that series, so HPLC still found the trait.

This is the common mistake, and it is easy to make. The index points to the trait, so the iron deficiency is missed. Or the iron deficiency is treated, and the trait is never looked for. The safe practice the tool gives: if the HPLC is borderline and the patient is iron deficient, correct the iron and repeat the HPLC.

4. How common is this in India?

Anaemia. Anaemia was dropped entirely from the National Family Health Survey 6, whose fact sheets were released on 29 May 2026 with no haemoglobin indicator at all, and the estimate has moved to the ICMR Diet and Biomarkers Survey. The most recent national figures therefore remain those of NFHS-5: 57.0 per cent of women aged 15 to 49, 25.0 per cent of men, 67.1 per cent of children aged 6 to 59 months.

The carrier state. The average beta-thalassaemia carrier frequency in India is 3 to 4 per cent, around 42 million carriers, and 10,000 to 15,000 children with thalassaemia major are born each year. A systematic review of 69 studies put the general population figure at 3.74 per cent and tribal groups at 4.6 per cent. Carrier rates are higher in Sindhi, Punjabi, Gujarati and Bengali communities and in several tribal groups.

And sickle cell disease. The National Sickle Cell Anaemia Elimination Mission, launched on 1 July 2023, is screening 7 crore people aged 0 to 40 across 278 districts in 17 states, with an elimination target of 2047. By July 2025 it had screened 6 crore and identified 16.7 lakh carriers. It is sickle cell specific: thalassaemia prevention still sits under the 2016 national haemoglobinopathies guidelines and state programmes rather than a comparable national mission.

“Why does a carrier rate matter to one patient?” Because finding a trait is never only about the patient in front of you. It is a reason to test the partner before a pregnancy, and to counsel the family.

Back to Udupi

Our student did not need a stronger iron tablet. Her indices pointed to beta-thalassaemia trait, and the tool directed the next two investigations: haemoglobin HPLC and a ferritin. The Indian national guideline reads a haemoglobin A₂ of 4.0 to 8.0 per cent as diagnostic of the trait. Because she was about to marry, the most useful test after hers was her fiance’s.

Try this

A 30-year-old man has an MCV of 70 fL and a red cell count of 5.0 × 10¹²/L. His Mentzer index is 14.0. The published cut-off is 13, and the Manipal cut-off is 14.07. Which way does the index point, and what do you do? Illustrative case.

Answer. Above 13, the published cut-off favours iron deficiency. Below 14.07, the Manipal cut-off favours the trait. The two disagree, and the tool shows both. Do not act on one index alone. Send the HPLC and a ferritin, and let them decide.

Take-home points

• A microcytic anaemia with a high red cell count should make you think of a trait before iron.
• The published cut-offs travel badly to Indian patients; where the local and published cut-offs disagree, test further.
• A carrier can also be iron deficient; if the HPLC is borderline, correct the iron and repeat it.
• No index diagnoses: HPLC and ferritin settle it.
• Finding a trait means testing the partner and counselling the family.

Declaration: the author built and maintains the tool. It is free to use. The figures in this article are those the tool carried in its Evidence tab on 4 November 2026, each from the source the tool names. The illustrative cases follow the tool’s rules; check the tool’s result for a real patient.

References

1. Mentzer WC Jr. Differentiation of iron deficiency from thalassaemia trait. Lancet. 1973;301(7808):882.
2. Srivastava PC, Bevington JM. Iron deficiency and-or thalassaemia trait. Lancet. 1973;301(7807):832.
3. Shine I, Lal S. A strategy to detect beta-thalassaemia minor. Lancet. 1977;309(8013):692-694.
4. Green R, King R. A new red cell discriminant incorporating volume dispersion for differentiating iron deficiency anemia from thalassemia minor. Blood Cells. 1989;15(3):481-491.
5. Sirdah M, Tarazi I, Al Najjar E, Al Haddad R. Evaluation of the diagnostic reliability of different RBC indices and formulas in the differentiation of the beta-thalassaemia minor from iron deficiency in Palestinian population. Int J Lab Hematol. 2008;30(4):324-330.
6. Ehsani MA, Shahgholi E, Rahiminejad MS, Seighali F, Rashidi A. A new index for discrimination between iron deficiency anemia and beta-thalassemia minor: results in 284 patients. Pak J Biol Sci. 2009;12(5):473-475.
7. Matos JF, Dusse LMS, Borges KBG, de Castro RLV, Coura-Vital W, Carvalho MG. A new index to discriminate between iron deficiency anemia and thalassemia trait. Rev Bras Hematol Hemoter. 2016;38(3):214-219.
8. 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(11):1883-1894.
9. Kumar A, Saha D, Kini J, Murali N, Chakraborti S, Adiga D. The role of discriminant functions in screening beta-thalassemia trait and iron deficiency anemia among laboratory samples. J Lab Physicians. 2017;9(3):195-201.
10. Madan N, Sikka M, Sharma S, Rusia U. Coexisting iron deficiency in patients with beta thalassaemia trait. Indian J Hematol Blood Transfus. 2012.
11. Colaco S, Colah R, Nadkarni A. Significance of borderline HbA₂ levels in beta thalassemia carrier screening. Sci Rep. 2022;12:5414.
12. Ministry of Health and Family Welfare, Government of India. Prevention and control of hemoglobinopathies in India: thalassemias, sickle cell disease and other variant hemoglobins. New Delhi: National Health Mission; 2016.
13. World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. Geneva: WHO; 5 March 2024.
14. Ministry of Health and Family Welfare, Government of India. Anemia Mukt Bharat: operational guidelines for programme managers. New Delhi: National Health Mission; 2018.
15. World Health Organization. WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. Geneva: WHO; 21 April 2020.
16. Riley RS, Ben-Ezra JM, Tidwell A, Romagnoli G. Reticulocyte analysis: methods and clinical applications. Reproduced in the American Journal of Clinical Pathology maturation-factor table used here; the underlying observation is Hillman RS. Characteristics of marrow production and reticulocyte maturation in normal man in response to anemia. J Clin Invest. 1969;48(3):443-453.
17. Sachdev HS, Porwal A, Acharya R, et al. Haemoglobin thresholds to define anaemia in a national sample of healthy children and adolescents aged 1-19 years in India: a population-based study. Lancet Glob Health. 2021;9(6):e822-e831.