Out of 89 stone formers with idiopathic
hypercalciuria, 51 remained hypercalciuric on a low
calcium diet over 5 days: a renal leak of
calcium could thus have been suspected in them. Dietary factors such as high
sodium or high animal
protein intake, and metabolic factors such as
obesity with or without
hyperinsulinemia, which all might account for the
hypercalciuria of these patients, have been evaluated. This evaluation revealed conditions known to be associated with
hypercalciuria in 37 of these 51 patients: 15 had
hypercalciuria related to a high
sodium intake, 7 had severe hyperuricosuria (greater than 1 g/24 h) reflecting a high animal
protein intake, 20 were obese (greater than 120% of ideal weight) with (7 cases) or without (13 cases) concomitant high fasting plasma level of
insulin (greater than 18 microU/ml). A careful retrospective analysis of the intravenous pyelograms disclosed
medullary sponge kidneys in 8 cases which had remained undiagnosed so far. One of them was studied histologically. Only 14 out of 51 patients had an otherwise unexplained
hypercalciuria on a low
calcium diet. It is concluded that dietary causes appear to play a key role in 'idiopathic'
hypercalciuria, that the incidence of a primary renal leak of
calcium among idiopathic stone formers is much smaller than initially thought, and that this condition can hide unrecognized
medullary sponge kidneys.