In microcytic anemia, which red blood cell index is typically reduced?

• A. Mean Corpuscular Volume (MCV)
• B. Mean Corpuscular Hemoglobin (MCH)
• C. Hemoglobin Concentration per Cell
• D. Red Blood Cell Distribution Width (RDW)

Answer: (A)

The main idea is that microcytic anemia is defined by smaller-than-normal red blood cells. The mean corpuscular volume measures the average size (volume) of those cells, so when the cells are smaller, this average drops. That’s why the mean corpuscular volume is typically reduced in microcytic anemia.

The other indices tell different things. Mean corpuscular hemoglobin measures how much hemoglobin is in each cell and can be reduced if cells are hypochromic, but size reduction is the hallmark of microcytosis, not just hemoglobin per cell. Hemoglobin concentration per cell (MCHC) reflects hemoglobin density inside cells and can be normal in some microcytoses. Red blood cell distribution width (RDW) reflects variation in cell size; it can be normal or increased depending on the cause and isn't the defining feature of microcytosis.