The index is calculated from the results of a complete blood count. If the quotient of the mean corpuscular volume (MCV, in fL) divided by the red blood cell count (RBC, in Millions per microLiter) is less than 13, thalassemia is said to be more likely. If the result is greater than 13, then iron-deficiency anemia is said to be more likely.
The principle involved is as follows: In iron deficiency, the marrow cannot produce as many RBCs and they are small (microcytic), so the RBC count and the MCV will both be low, and as a result, the index will be greater than 13. Conversely, in thalassemia, which is a disorder of globin synthesis, the number of RBCs produced is normal, but the cells are smaller and more fragile. Therefore, the RBC count is normal, but the MCV is low, so the index will be less than 13.
- Mentzer WC (April 1973). "Differentiation of iron deficiency from thalassaemia trait". Lancet. 1 (7808): 882. doi:10.1016/S0140-6736(73)91446-3. PMID 4123424.
- Ntaios G, Chatzinikolaou A, Saouli Z, et al. (July 2007). "Discrimination indices as screening tests for beta-thalassemic trait". Ann. Hematol. 86 (7): 487–91. doi:10.1007/s00277-007-0302-x. PMID 17476506.
- Joseph Mazza (15 January 2002). Manual of clinical hematology. Lippincott Williams & Wilkins. pp. 152–. ISBN 978-0-7817-2980-2. Retrieved 4 June 2010.