Interrelations of radiocalcium absorption tests and their clinical relevance.

Intestinal absorption of radiocalcium from an oral test dose was measured in 84 patients with various disorders of bone and calcium metabolism. In each subject, five different methods were used to assess intestinal absorption and the estimates obtained were compared inter- and intra-individually. The whole-body counting technique was chosen as reference method and as a basis for comparison of the other four estimates. Plasma levels of radiocalcium after oral administration seem to provide a simple and rapid test which may serve its purpose in various clinical situations. Fractional intestinal calcium absorption can be assessed equally well by the whole-body counting technique, the double-isotope method or the double-isotope deconvolution technique, since these methods yield comparable results. The deconvolution technique additionally provides a quantitative description of the absorptive process of calcium with respect to time.