Mentzer Index Calculator

What Is the Mentzer Index?

The Mentzer index is a simple ratio used to distinguish iron deficiency anemia from thalassemia trait in patients with microcytic anemia. It divides mean corpuscular volume (MCV) by red blood cell count (RBC). Because thalassemia produces smaller red cells in greater numbers while iron deficiency reduces both cell size and count, the index helps guide further testing before ordering hemoglobin electrophoresis or iron studies. Use the Iron Deficiency Calculator for iron status assessment and the Lymphocyte Count Calculator for related complete blood count parameters.

Mentzer Index Formula

Mentzer index = MCV (fL) / RBC count (million/mm³ or 10⁶/µL). Enter values from a standard complete blood count. An index below 13 suggests thalassemia trait is more likely than iron deficiency anemia. An index above 13 favors iron deficiency. An index of exactly 13 is inconclusive and warrants additional testing such as serum ferritin, iron studies, and hemoglobin electrophoresis. The Mentzer index is a screening tool, not a definitive diagnosis.

Thalassemia vs. Iron Deficiency

Iron deficiency anemia develops from insufficient iron stores, causing low MCV and low RBC count with high Mentzer index. Thalassemia trait produces microcytosis through reduced hemoglobin synthesis per cell, but the bone marrow compensates with increased RBC production, yielding a lower Mentzer index. Other discriminant indices exist (Green and King, Shine and Lal) and perform similarly. Always confirm with ferritin, transferrin saturation, and hemoglobin electrophoresis before starting iron therapy or genetic counseling.