From an MCV Article
What might an elevated MCV indicate?
MCV stands for 'mean corpuscular volume', one of the values taken as part of a complete blood count. A group of tests performed on a small amount of blood that provides information about the quantity and quality of each type of blood cell. The MCV is an evaluation of the average volume of each red cell. A high MCV (mean corpuscular volume) is common in MDS and in severe aplastic anemia. MCV is almost invariably elevated also in PNH.
A high MCV is a sign of bone marrow stress in these patients. It does not have independent prognostic significance. It does not warrant treatment per se, unless it is actually due to deficiencies in vitamin B12 or folic acid.
Folic acid or vitamin B12 deficiency should be excluded as causes for the elevated MCV; both of these conditions can cause low blood counts. An increased rate of red blood cell distruction (hemolysis)should also be excluded by checking the reticulocyte count(reticulocytes are larger than mature red blood cells). Hemolysis requires specific treatment. If these conditions are excluded, the high MCV can be attributed to the MDS or aplastic anemia.
The oxygen carrying cells in our body. These bring oxygen to our tissues, and are the most numerous of the blood cells. If these conditions are excluded, the high MCV can be attributed to the MDS or aplastic anemia. It is common in both conditions.