Etiology and diagnostic evaluation of macrocytosis.

BACKGROUND: Elevation of mean cell volume (MCV) is a common clinical problem, but the etiologic spectrum and optimal diagnostic evaluation of macrocytosis are not well defined.

METHODS: We studied 300 consecutive hospitalized adult patients with MCV values > or = 100 fL. Assessment included complete blood counts, morphologic review, liver function tests, and levels of serum cobalamin (Cbl), methylmalonic acid, and total homocysteine.

RESULTS: The most common cause of macrocytosis was drug therapy, followed by alcohol, liver disease, and reticulocytosis. Megaloblastic hematopoiesis accounted for less than 10% of cases. MCV values > 120 fL were usually caused by Cbl deficiency. Anisocytosis, macro-ovalocytosis, and teardrop erythrocytes were most prominent in megaloblastic hematopoiesis. Elevated levels of serum methylmalonic acid and total homocysteine were useful in the diagnosis of Cbl deficiency.

CONCLUSIONS: Drugs and alcohol are the most common causes of macrocytosis in hospitalized patients in a New York City teaching hospital. We have formulated tentative guidelines for the evaluation of high MCV values in this setting.