Mentzer Index

The Mentzer index is used to differentiate iron deficiency anemia from beta thalassemia. If a CBC indicates microcytic anemia, these are two of the most likely causes, making it necessary to distinguish between them.

It is calculated from the results of a complete blood count. If the quotient of the mean corpuscular volume divided by the red blood cell count is less than 13, thalassemia is more likely. If the result is greater than 13, then iron-deficiency anemia is more likely.

It was described in 1973.

This test helps in differentiating iron deficiency from thalassemia. In iron deficiency, the marrow cannot produce as many RBCs and they are small (microcytic), so the RBC count will be low along with the MCV, and as a result, Mentzer's index is not as low, >13 Comparatively, in thalassemia, which is a disorder of globin synthesis, RBC production is preserved, but the cells are smaller and more fragile. Therefore, the RBC count is normal with a low MCV and the Mentzer's index is <13.

It is also important to note that the test has a high sensitivity and low specificity. In a lot of cases, the index may fall in between 11 and 13, such cases a peripheral blood smear and iron studies would help to differentiate iron deficiency from thalassemia.