Tracer Studies of Intestinal Calcium Absorption in Man

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Abstract
Absorption of calcium has been estimated in 77 subjects, including 43 normal individuals, by 159 studies under varying conditions of diet and therapy. The techniques used were those of metabolic balance, oral 47Ca administration, intravenous 45Ca and 47Ca, and combinations of these. The results obtained by these procedures have been examined with a view to correlate values obtained in different laboratories. The possible errors inherent in each estimate have been discussed. No single "rapid" procedure is ideal for all clinical situations. The most reliable values may be obtained by the use of combined oral and intravenous tracers under conditions of complete metabolic balance collections. The simplest technique of screening for calcium malabsorption is the estimation of in vivo retention of an oral dose 5 hr after administration of the tracer. The measurements obtained suggest that osteoporosis in males is of different etiology from that of females with fixed absorption and urinary excretion of calcium. Absorption of calcium in this small population of female patients with osteoporosis was within the range of normals.