Vitamin B12 can bind two carrier proteins in the digestive tract, haptocorrin (R binder) and intrinsic factor, but only its binding to intrinsic factor allows its absorption. A malabsorption of vitamin B12 is observed in about 30% of adult patients with exocrine pancreatic insufficiency, using the Schilling test. None of the hypotheses that have tried to explain this malabsorption are entirely satisfactory. A failure to degrade haptocorrin can prevent the binding of vitamin B., to intrinsic factor. It has also been suggested that pancreatic secretion could modify the structure of intrinsic factor, enabling the uptake of the vitamin B12 intrinsic factor complex by the ileum. Other factors can also affect the binding of vitamin B., to intrinsic factor, such as the gastric pH and bile. The Schilling test is abnormal in nearly all cases of cystic fibrosis. One explanation could be the gastric hyperacidity observed in this disease. Despite the frequency of abnormal Schilling tests, vitamin B., deficiency is very rare in cases of exocrine pancreatic dysfunction, in adults as well as in children with cystic fibrosis. The assimilation of this vitamin with a tracer included in food instead of the crystalline labeled cobalamin used in the Schilling test remains to be investigated.
Address correspondence and are print requests to Dr. J. L. Gudant at Biochemistry-Immunology, INSERM U 308, Facult6 de Medecine, Avenue de la Foret de Haye-Bat. C 2e étage B.P. 184, 54505 Vandoeuvre-les-Nancy Cćdex, France.
Manuscript received July 31, 1989; revised manuscript; revised manuscript accepted accepted on January 16, 1990.
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