Gastrointestinal absorption of calcium was measured in patients who had formed renal stones containing calcium by a simple technique based on external counting of the forearm 47Ca radioactivity. The total amount of dietary calcium absorbed was estimated as the product of dietary calcium and fractional calcium absorption. Mean fractional calcium absorption (from a 200-mg calcium load) in control subjects and in patients with normal urinary calcium was 0.456 ± .087 (SD) and 0.460 ± .079, respectively. Estimated calcium absorbed per day in these two groups always exceeded the urinary excretion of calcium. In the patients with idiopathic hypercalciuria, the fractional calcium absorption was elevated (0.697 ± .070), and the estimated calcium absorbed per day always exceeded the urinary excretion of calcium; hyperabsorption could therefore fully account for the hypercalciuria. Of 11 patients subsequently shown to have normocalcemic hyperparathyroidism, hyperabsorption of calcium was encountered in 8. In 6 of these, the estimated calcium absorbed per day was less than the urinary calcium. The results suggest that some patients with normocalcemic hyperparathyroidism differ from those with idiopathic hypercalciuria, in that the hypercalciuria cannot be attributed to intestinal hyperabsorption of calcium alone.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical