Incidence of normocalcemic hyperparathyroidism in idiopathic hypercalciuria: Evaluation by dietary calcium deprivation test

Calcium metabolism was studied in 37 patients with 'idiopathic hypercalciuria' on a home diet and after 10 days of low calcium dietary intake (<400 mg/24h). After low calcium intake, urinary calcium excretion returned to within normal limits in 70% of the cases. In the group of patients which failed to respond to calcium restriction, TmPO 4/GFR values were reduced and, furthermore, in 20% of them plasma iPTH and urinary cAMP levels were increased. These data seem to indicate that: the incidence of absorptive hypercalciuria is higher than hypercalciuria of renal origin; normocalcemic hyperparathyroidism due to primary calcium leak is present only in a limited number of cases and, consequently, hypercalciuria secondary to renal phosphate leak is a rather frequent occurrence.