Macrocytic anemias are less commonly encountered than normocytic or microcytic anemias. These anemias may be caused by marrow failure such as aplastic anemia and myelodysplasis, or caused by deficiencies of vitamin B12 or folic acid; or caused by autoimmune hemolysis or cold agglutinins. A mild degree of macrocytosis with a normal RDW is commonly seen as a result of alcohol abuse. The MCV is greater than 100 fl. in macrocytic anemia.
The macrocytic anemias may be further subdivided based upon the degree to which the MCV is raised and the presence of megaloblastic production in the bone marrow.
Slight increase in MCV:
MCV > 100
- due to the presence of retics
- in some instances of aplastic anemia
In all cases the red cell precursors in the marrow are normal in morphology.
Moderate increase in the MCV:
MCV > 105
- liver disease
Marked increase in the MCV:
MCV > 110 fl.
- megaloblastic due to the lack of vitamin B-12 or folic acid.