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

Abstract
A procedure-is suggested for the assay of preparations of intrinsic factor by measuring the urinary excretion of radioactivity following dosage with vitamin B12 labeled with Co60. It was found important to use more than one "flushing" dose of unlabeled vitamin 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. Injection of large amounts of unlabeled vitamin B12 appeared to decrease the uptake of small doses of labeled vitamin B12 when subsequently given orally. There appeared to be some proportionality between the dosage of intrinsic factor and the amount of radioactivity excreted in the test.