Immunologic Approaches to Malabsorption of Vitamin B12

Absorption of Vitamin B12alone or with added intrinsic factor was impaired in three patients with vitamin B12malabsorption, two of whom had megaloblastic anemia, thus supporting the diagnosis of intestinal malabsorption rather than pernicious anemia. Yet, presence of serum autoantibodies to parietal cells or intrinsic factor or both indicated concomitant pernicious anemia. Absorption of vitamin B12in the presence of intrinsic factor was restored in two patients by therapy with cyanocobalamin, suggesting that the initial absorptive abnormalities were induced by deficiency of this vitamin. Autoantibodies to parietal cells were also present in one of three patients withDiphyllobothrium latum-caused vitamin B12deficiency. She had concomitant pernicious anemia. Immunologic tasks are valuable aids in differentiating disorders of vitamin B12malabsorption.