, Volume 24, Issue 5, pp 397-402

Clinically significant vitamin B12 deficiency secondary to malabsorption of protein-bound vitamin B12

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Protein- (chicken serum) bound [57Co]cyanocobalamin absorption was evaluated in five hypochlorhydric patients who had developed B12 deficiency despite having normal absorption of unbound crystalline vitamin B12. All five patients had decreased urinary excretion of protein-bound B12 (0.06–0.34%) as compared to twelve normal controls (0.61–5.6%), P<.001. Improvement in protein-bound B12 absorption in four of the five patients occurred with the exogenous administration of hydrochloric acid, pepsin, gastric intrinsic factor, or a combination thereof. Vitamin B12 deficiency developing in the setting of hypochlorhydria may result from deficiency of acid-peptic digestion of B12 bound to protein and/or a relative deficiency of intrinsic factor. This digestive defect is not detected with tests which measure the absorption of unbound crystalline B12 but is detected by a simple test which employs B12 bound to chicken serum as the form of protein-bound B12.

Dr. King is the recipient of a Research Associate Award from the Veterans Administration. During the performance of these studies Dr. Toskes was a Clinical Investigator with the Veterans Administration.
Supported in part by Grant RR-82 from the National Institutes of Health.
Presented in part at the Annual Meeting of the American Gastroenterology Association in Toronto, Canada, May 1977.