[So-called "renal" idiopathic hypercalciuria most often has a dietary origin].

Among renal stone formers with idiopathic hypercalciuria, patients who remain hypercalciuric despite low calcium intake have often been regarded as having a primary renal leak of calcium, i.e. renal hypercalciuria. However, at any given intake of calcium, dietary factors other than calcium can generate hypercalciuria, e.g. high intakes of sodium, of animal protein or of carbohydrates, or obesity itself. Thus, the incidence of renal hypercalciuria among stone formers has probably been overestimated. To address this issue, the aforementioned dietary and/or metabolic factors have been evaluated in 51 stone formers with idiopathic hypercalciuria refractory (i.e. U-Ca. V greater than 250 mg/24 h) to 5 days on low calcium intake (max. 400 mg/day). In 15 patients (all had U-Na. V greater than 200 mmol/24 h), U-Ca.V was within the 95% confidence limits of a nomogram U-Ca.V versus U-Na.V, suggesting that their idiopathic hypercalciuria was related, at least in part, to the high sodium intake. 7 patients had severe hyperuricosuria (greater than 1 g/24 h) suggesting high animal protein intake. 20 patients were obese (greater than 120% ideal weight) with (7 cases) or without (13 cases) concomitant fasting hyperinsulinemia (greater than 18 microU/ml). In addition, a careful retrospective analysis of intravenous pyelograms disclosed medullary sponge kidneys in 8 cases which had remained undiagnosed so far; in one of them histological confirmation was obtained after surgical removal of a renal pole and a radiologico-histological comparison. Thus, only 14 out of 51 patients had an otherwise unexplained idiopathic hypercalciuria on low calcium intake.(ABSTRACT TRUNCATED AT 250 WORDS)