MCV, also known as mean red blood cell volume, is an indicator in routine blood tests. This is called macrocytic anemia. There are two most common diseases, one is myelodysplastic syndrome and the other is megaloblastic anemia. If there is a deficiency of folic acid or vitamin B12, the diagnosis of megaloblastic anemia can be made. If the three anemias are normal, a bone marrow aspiration should be performed to rule out myelodysplastic syndrome.