Plasma Radioactivity following Oral Administration of 57Co-Labelled Vitamin B12

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Abstract
Levels of plasma radioactivity were measured 8 1/2 hours after an oral dose of 1 μg of 57Co-labelled vitamin B12. The oral test dose was followed after 2 hours by a large parenteral dose (1,000 μg) of non-radioactive vitamin B12. The results of this test have been compared with the results of the urinary excretion (Schilling test) in 14 normal subjects and in 14 patients suffering from pernicious anaemia (in 10 of whom the test was later repeated with added hog intrinsic factor). Very low levels of plasma radioactivity were found in patients suffering from pernicious anaemia (less than 0.21% of the administered dose per litre of plasma); much higher levels of radioactivity (more than 0.95% of administered radioactivity per litre of plasma) were found in normal subjects. Levels of plasma radioactivity approaching but not quite reaching the normal range were found in patients with pernicious anaemia when the test was repeated with the addition of hog intrinsic factor. It is concluded that this test provides a simple, rapid, semi-quantitative method of assessing the absorption of vitamin B12 from the gastro-intestinal tract. In our view, it is likely to supplant the Schilling test for routine use in a busy general hospital.