Medline ® Abstract for Reference 12

B12 deficiency is the leading cause of megaloblastic anemia and though more common in the elderly, can occur at any age. Clinical disease caused by B12 deficiency usually connotes severe deficiency, resulting from a failure of the gastric or ileal phase of physiological B12 absorption, best exemplified by the autoimmune disease pernicious anemia. There are many other causes of B12 deficiency which range from severe to mild. Mild deficiency usually results from failure to render food B12 bioavailable or from dietary inadequacy. Though rarely resulting in megaloblastic anemia, mild deficiency may be associated with neurocognitive and other consequences. B12 deficiency is best diagnosed using a combination of tests since none alone is completely reliable. The features of B12 deficiency are variable and may be atypical. Timely diagnosis is important and treatment gratifying. Failure to diagnose B12 deficiency can have dire consequences, usually neurological. This review is written from the perspective of a practicing hematologist.