Low serum cobalamin levels occur frequently in the acquired immune deficiency syndrome and related disorders.

Low serum cobalamin levels in 10 patients with AIDS or AIDS-related complex led us to also prospectively survey 40 homosexual men in our AIDS clinic. 8 of the latter (20%) had low cobalamin values. We found no evidence of megaloblastic changes in the blood or bone marrow. Assessment disclosed malabsorption of cobalamin in only 1 of 6 cases tested for it. 6 of the patients were treated with cobalamin and had no hematologic response. It appears that low serum cobalamin levels in AIDS and related disorders do not usually represent overt cobalamin deficiency. While malabsorption is occasionally responsible for the low cobalamin level, in most cases the cause is unknown and may reflect a serum abnormality similar to that in multiple myeloma. AIDS and related disorders should be considered in the differential diagnosis of unexplained low cobalamin levels.