DETERMINATION OF ABSORPTION OF VITAMIN B12 BY A DOUBLE ISOTOPE TRACER TECHNIQUE.

Abstract

The conventional methods for the quantitative estimation of the absorption of labeled vitamin B12 require either a prolonged collection of faeces ( 1 ) or a complete 24-hour urinary collection, as in the Schilling's test (2) . It is usually necessary to admit the patient to a hospital for this investigation; even then, a reliable total collection of urine or faeces is impossible without intelligent cooper ation from the patient and the nursing staff. Furthermore, the Schilling's test, which is by far the most commonly employed procedure, does not give a true quantitative measure of vitamin B12 absorption, as it measures only that per cent of the administered dose which is flushed out into the urine after a large paren teral dose of stable vitamin B19. This flushing dose also hinders subsequent hema tological studies. The new technique described in this paper gives an accurate estimate of vitamin B19 absorption by counting radioactivity in an aliquot of a random sample of faeces. An unabsorbable marker in the form of 51Cr labeled chromic oxide is administered orally with 5sCo labeled vitamin B,2. The ratio of the two radioisotopes in the administered dose is compared with the ratio of these isotopes in a sample of faeces collected after 24 or 48 hours. Any change in the ratio would be due to the absorption of labeled vitamin B,9 and the proportion of 58Co labeled vitamin B19 absorbed is calculated by reference to the 51Cr excreted.