The erythrocyte coefficient of variation is an indicator of the width of the red blood cell volume distribution, which is also an indicator of the homogeneity of the red blood cell size in the peripheral blood. A high erythrocyte coefficient of variation indicates that the red blood cells in the peripheral blood are not uniform in size, a condition most commonly seen in clinical practice as iron deficiency anemia. Because of iron deficiency, red blood cells are unable to synthesize hemoglobin normally using iron, resulting in a reduction in the size of some red blood cells, which results in uneven red blood cell volume, ranging from very small cells to large cells, resulting in a significantly higher erythrocyte coefficient of variation. Another disease that can be differentiated by the erythrocyte coefficient of variation is thalassemia, because thalassemia is also a microcytic hypochromic anemia, but the erythrocyte coefficient of variation is not increased in thalassemia patients. Therefore, in the case of microcytic hypochromic anemia, iron deficiency anemia is the one with a high RVF and thalassemia is the one with a low RVF.