Etiology and diagnostic evaluation of macrocytosis

Background: Elevation of mean cell volume (MCV) is a common clinical proble m, but the etiologic spectrum and optimal diagnostic evaluation of macrocyt osis are not well defined. Methods: We studied 300 consecutive hospitalized adult patients with MCV values greater than or equal to 100 fL. Assessment included complete blood counts, morphologic review, liver function tests, and levels of serum cobalamin (Cbl), methylmalonic acid, and total homocyst eine. Results: The most common cause of macrocytosis was drug therapy, foll owed by alcohol, liver disease, and reticulocytosis. Megaloblastic hematopo iesis accounted for less than 10% of cases. MCV values > 120 fL were usuall y caused by Cbl deficiency. Anisocytosis, macro-ovalocytosis, and teardrop erythrocytes were most prominent in megaloblastic hematopoiesis. Elevated l evels of serum methylmalonic acid and total homocysteine were useful in the diagnosis of Cbl deficiency. Conclusions: Drugs and alcohol are the most c ommon causes of macrocytosis in hospitalized patients in a New York City te aching hospital. We have formulated tentative guidelines for the evaluation of high MCV values in this setting.