Subtle cobalamin malabsorption in a vegan patient: evolution into classic pernicious anemia with anti-intrinsic factor antibody.

Classic pernicious anemia with abnormal Schilling test results developed in a previously described vegan patient who had coexisting subtle cobalamin malabsorption (demonstrable by abnormal ovalbumin-cobalamin absorption test results but normal Schilling test results). This suggests that the ovalbumin-cobalamin absorption test or a modified version may serve as a prodromal phenomenon to identify patients at risk for developing pernicious anemia. The patient's transformation was also accompanied by the appearance of serum anti-intrinsic factor antibody. A modified assay retrospectively detected this antibody a year earlier than did the standard assay, indicating that such modification enhances the sensitivity of this useful test.