The spectrum of vitamin B12 deficiency.

Low serum vitamin B12 levels are not uncommon in the elderly. Patients with vitamin B12 deficiency manifest a spectrum of clinical findings. Pernicious anemia and malabsorption syndrome are the usual causes of vitamin B12 deficiency. Pernicious anemia is confirmed by the presence of intrinsic factor blocking antibody or abnormal results on the Schilling test. Patients with neuropsychiatric symptoms of vitamin B12 deficiency may have a normal Schilling test and no evidence of macrocytic anemia. In such patients, vitamin B12 deficiency is confirmed by determining serum levels of homocysteine and methylmalonic acid.