Spurious Schilling test results obtained with intrinsic factor enclosed in capsules

Abstract

Three urinary excretion tests of vitamin B12 absorption were done in 12 patients with classic pernicious anemia. The 24-hour urinary excretion of radioactivity was 2.1% +/- 0.7% (mean +/- SEM) of the ingested dose of cyanocobalamin-57 Co. When cyanocobalamin-57 Co was mixed with hog intrinsic factor in water, excretion increased to 15.6% +/- 1.6%. When cyanocobalamin-57 Co and intrinsic factor were given in two separate capsules, which is now a frequent practice, excretion was 9.5% +/- 2.2%. In 6 patients, use of the results obtained with capsules could have led to an incorrect diagnosis. When cyanocobalamin-57 Co and intrinsic factor are given in separate capsules, binding of radioactive vitamin to intrinsic factor may be incomplete due to inadequate mixing in the stomach or to binding of intrinsic factor to blocking antibody in the gastric juice. The classic technique in which intrinsic factor and cyanocobalamin-57 Co are mixed in water before administration should be used.