Anisocytosis is a general term used to describe increased variation in size of the red cell population present on a blood smear. The normal size of red cells varies from approximately 6 to 9 microns. Notice that normal, small and large cells can be seen in this field. Since several populations of cells are present, this abnormality will not be reflected in the MCV value (However, it will show up as an increase in the RDW, which is a measure of red cell size variation.) As the severity of the anemia increases, the amount of significant anisocytosis present also increases.