Comparison between the fractional isotopic calcium absorption and an oral calcium tolerance test.

In 27 subjects with several disorders of calcium metabolism, the fractional intestinal absorption of 47CaCl2 was rather poorly correlated with the urinary output of calcium or with the maximal increase of serum calcium after an oral calcium load. Conversely, a good correlation was observed with the product of these parameters. We propose that this product be used as an estimate of intestinal calcium absorption when a radioisotopic method is not available.