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Vitamin B12 Deficiency

Vitamin B12 deficiency can cause macrocytic anemia and neuropsychiatric disorders. While diagnosis is typically based on low serum B12 levels, about half of subclinical cases have normal levels. More sensitive tests measure methylmalonic acid and homocysteine levels. Oral B12 supplementation is a safe and effective treatment for B12 deficiency, even without intrinsic factor or in diseases affecting absorption in the ileum. Follow-up testing two to three months after treatment can check for correction of mild deficiency.

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 Vitamin B12 deficiency is a common cause of macrocytic anemia and has been implicated in a spectrum of neuropsychiatric disorders  The role of B12 deficiency in hyperhomocysteinemia and the promotion of atherosclerosis is only now being explored.  Diagnosis of vitamin B12 deficiency is typically based on measurement of serum vitamin B12 levels; however, about 50 percent of patients with subclinical disease have normal B12 levels.
 A more sensitive method of screening for vitamin B12 deficiency is measurement of serum methylmalonic acid and homocysteine levels, which are increased early in vitamin B12 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 B12 is a safe and effective treatment for the B12 deficiency state.  Even when intrinsic factor is not present to aid in the absorption of vitamin B12 (pernicious anemia) or in other diseases that affect the usual absorption sites in the terminal ileum, oral therapy remains effective.
Clinical Manifestations Hematologic  Megaloblastic anemia  Pancytopenia (leukopenia, thrombocytopenia) Neurologic  Paresthesias  Peripheral neuropathy  Combined systems disease (demyelination of dorsal columns and corticospinal tract) Psychiatric
Follow-Up  Vitamin B12 deficiency associated with severe anemia, correction of the deficiency state should lead to a marked reticulocytosis in one to two weeks  In mild vitamin B12 deficiency, we recommend repeat measurements of serum vitamin B12, homocysteine, and methylmalonic acid levels two to three months after initiating treatment.