The use of a test for the differential diagnosis of hypercalciuria

28 renal stone formers (18 men and 10 women) with idiopathic hypercalciuria (IH) and 27 controls have been subjected to a test proposed for the diagnosis of absorptive, resorptive and renal hypercalciurias. Fasting serum calcium concentration, urinary calcium and cyclic AMP excretion were measured after overnight fasting and an oral load of calcium. Absorptive hypercalciuria was demonstrated in 14 patients. High fasting urinary calcium first suggested resorptive or renal hypercalciurias in 5 other patients, but since fasting urinary calcium was normalized following cellulose phosphate therapy, absorptive hypercalciuria was more likely. Renal hypercalciuria was a possibility in 1 single case. Both fasting and post-load urinary calcium were normal in 7 men and 1 woman. The test did not appear as useful as expected since it was of no diagnostic value in about 30% of the cases and erroneously suggested resorptive or renal hypercalciuria in about 15% of the cases. On the other hand it indicated that absorptive IH is common and renal IH exceptional.