The MCV (Mean Corpuscular Volume) reflects the size of red blood cells by expressing the volume occupied by a single red blood cell.
Cells of normal size are called normocytic, smaller cells are microcytic, and larger cells are macrocytic. These size categories are used to classify anemias. Normocytic anemias have normal-sized cells and a normal MCV; microcytic anemias have small cells and a decreased MCV; and macrocytic anemias have large cells and an increased MCV. Under a microscope, stained red blood cells with a high MCV appear larger than cells with a normal or low MCV.
Normocytic anemia (normal MCV) can be caused by kidney and liver disease, bone marrow disorders, or excessive bleeding or hemolysis of the red blood cells.
Increased readings may indicate macrocytic anemia (high MCV) or B6 or Folic Acid deficiency.
Lack of iron in the diet, thalassemia (a type of hereditary anemia), and chronic illness are the most common causes of microcytic anemia (low MCV).
this information comes from the following website: http://www.saanendoah.com/hemo-mcv.html