An Improved Urinary Excretion Test as an Assay for Intrinsic Factor. ∗

Abstract

Summary

A procedure is suggested for the assay of preparations of intrinsic factor by measuring the urinary excretion of radioactivity following dosage with vit. B₁₂ labeled with cobalt 60. It was found important to use more than one “flushing” dose of unlabeled vit. B₁₂ to produce maximum excretion of radioactivity. By use of this precaution, the same patient could be used for assaying several preparations of intrinsic factor in succession. The injection of large amounts of unlabeled vit. B₁₂ appeared to decrease the uptake of small doses of labeled vit. B₁₂ when subsequently administered orally. There appeared to be some proportionality between the dosage of intrinsic factor and the amount of radioactivity excreted in the test.