1) Pathology 
Macrocytosis is the enlargement of red blood cells with near-constant hemoglobin concentration, and is defined by a mean corpuscular volume (MCV) of greater than 100 femtolitres (the precise criterion varies between laboratories). The enlarged erythrocytes are called macrocytes or megalocytes (both words have roots meaning `big cell`). == Causes.....
<haematology> Macrocytosis is enlargement of the red blood cells as defined by a red cell mean corpuscular volume (MCV) of greater than 100 fl. ... Macrocytosis is present in 1 to 4 % of the adult population. The most common cause is alcoholism. Other causes include: nutritional deficiencies (B12 and folate), chemotherapy, drug side effects, ...
(mak″ro-si-to´sis) macrocythemia.
Abnormally large red blood cells.
Type: Term Pronunciation: mak′rō-sī-tō′sis Synonyms: macrocythemia
[n] - the presence of macrocytes in the blood
macrocytosis 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 deficiencie...
noun the presence of macrocytes in the blood