Interpretation of Electronically Determined Macrocytosis

Macrocytosis identified by electronic erythrocyte sizing equipment is clinically significant whether anemia is present or not. Half of all patients with marked macrocytosis (mean corpuscular volume of 115 µm3 or greater) identified in a hospital hematology laboratory had deficiency of folic acid or vitamin B12, or both, as defined by erythrocyte folate and plasma B12 measurements. The proportion of deficient patients increased with increasing degrees of macrocytosis. Of patients without deficiency, half had liver disease or alcoholism with probable liver disease. Screening patients with marked macrocytosis for deficiency of folic acid and vitamin B12 has a high diagnostic yield and has become a routine procedure in our laboratory.