Absence of secondary hyperparathyroidism in most patients with renal hypercalciuria.

We examined parathyroid gland function in 47 patients with idiopathic hypercalciuria in an effort to determine whether serum levels of parathyroid hormone (PTH) and/or urinary excretion of cyclic adenosine monophosphate (cyclic AMP) can discriminate between the various forms of hypercalciuria. Although we could separate our 47 patients into two groups, 21 patients with renal hypercalciuria (RH) and 15 patients with absorptive hypercalciuria (AH), there remained a group of 11 patients who did not exactly correspond to either group. Basal serum PTH was normal in the two groups: for RH, 10.32 +/- 0.93; for AH, 11.43 +/- 1.10 microliter Eq/ml. Similarly, urinary cyclic AMP did not differ between the two groups: for RH, 4.88 +/- 0.5; for AH, 4.87 +/- 0.55 nmoles/dl/min GFR. Moreover, the response of the parathyroid glands to acute hypocalcemia produced by intravenous infusion of EDTA was not different among patients with AH, RH, and control subjects. Only one patient showed a marked increase of serum PTH in response to acute hypocalcemia, and the bone biopsy revealed increased osteoclastic resorption. In conclusion, our data show that serum levels of PTH and urinary cyclic AMP do not differentiate between the various forms of idiopathic hypercalciuria. The EDTA test demonstrated that secondary hyperparathyroidism is very uncommon in these patients.