Vitamin B12 deficiency

Vitamin B-12 (cobalamin) deficiency is a common cause of macrocytic anemia and has been implicated in a spectrum of neuropsychiatric disorders. The role of B-12 deficiency in hyperhomocysteinemia and the promotion of atherosclerosis is only now being explored. Diagnosis of vitamin B-12 deficiency is typically based on measurement of serum vitamin B-12 levels; however, about 50 percent of patients with subclinical disease have normal B-12 levels. A more sensitive method of screening for vitamin B-12 deficiency is measurement of serum methylmalonic acid and. homocysteine levels, which are increased early in vitamin B,, deficiency. Use of the Schilling test for detection of pernicious anemia has been supplanted for the most part by serologic testing for parietal cell and intrinsic factor antibodies. Contrary to prevailing medical practice, studies show that supplementation with oral vitamin B-12 is a safe and effective treatment for the B-12 deficiency state. Even when intrinsic factor is not present to aid in the absorption of vitamin B-12 (pernicious anemia) or in other diseases that. affect the usual absorption sites in the terminal ileum, oral therapy remains effective.