Measurement of absorption of vitamin B12 by whole-body gamma spectrometry.

PRESENT METHODS of measuring intestinal absorption of ra(lio-vitamin B12 iiuclude measurements of the radioactivity (1) in the feces, (2) over tIme liver projection, (:3) ii the serum, or (4) of the fraction of the al)sori'ed radioactivity excreted in the urine after the injection of a large amuiount of nonlabeled vitamin B12. \Vhile all these methods give clinically valuable results, Ilomie gives a quantitative measurement of the amount of B12 al)sori)e(l except the fecal excretion Inethodl, Illd this is clinically unpleasant, tiine-colisumuiimlg 111(1 dle1)ends 111)011 1 complete fecal collection. Absorption is determined most accurately by direct measurement of the itiliOtilit reniaining in the body after the unabsorbed radioactivity is excrete(1 in the feces. Stmch a technic is descril)ed in this paper. It is muiore quantitative and sinll)ler than tli(' Schilling test and reduces the alnount of radioactivity re-quire(1 per test. There is an inherent uncertainty in repetition of Schilling-type BB 2 absorption tests. The influemice of the cold B11 " flushing close " aiid of the retained radioactivity on a seccnn i ahsorptioii test is not kiuown. For this reason, to avoid)erturbing the steady state by a large flushing close and to increase the reliability , a direct niethod of measuring the retention of free vitamiii B12 aIi(l vitamimi B12 1)01111(1 to intrinsic factor was developed. It avoids repetition of the Schilling test i)ut sti 11 differentiates 1)etweell intrinsic factor deficiency an(l iuialahsorp-tion svndromiies. MATERIALS AND METhODS Vitaiiuin B lall eletl svith either Cot " t Co53, was tliluted with ummilabeled vitamin B to a specific activity of 0.2 ftc. 1tg. Absorptiomm tests were Performuled on 10 PatientS with irrelevant diseases, serving as comimparisons, and on 5 patients with deficient alusorptiomi of vitammuin B11 , either due to intestinal nialabsorption or to Pernicious anemuuia.