Changing etiology of macrocytosis. Zidovudine as a frequent causative factor.

Macrocytosis is most commonly associated with vitamin B12 and folate deficiencies, followed by alcoholism, liver disease, and malignant neoplasms. Many laboratories have observed that in recent years macrocytosis increasingly has been associated with zidovudine treatment of acquired immune deficiency syndrome. One hundred consecutive inpatients in a large metropolitan urban hospital with mean corpuscular volumes greater than 110 fL were studied; 44% were patients with acquired immune deficiency syndrome being treated with zidovudine, 19% were alcoholics, and 12% had malignant neoplasms. Only 3% were folate deficient and just 4% were vitamin B12 deficient. This study suggests that zidovudine has become the most common cause of macrocytosis in the hospitalized urban patient population and that vitamin B12 and folate deficiencies have decreased in proportion.