1. The presence of unusually large red cells in the blood.
2. A condition in which the erythrocytes are larger than normal; such as, in macrocytic anemia and some types of liver disease.

Macrocytosis is present in 1 to 4 percent of the adult population. The most common cause is alcoholism. Other causes include: nutritional deficiencies (B12 and folate), chemotherapy, drug side effects, haemolysis, liver dysfunction, myelodysplasia, as well as, hypothyroidism.