Parathyroid function in idiopathic hypercalciuria — response to oral calcium tolerance test.

Abstract

Idiopathic hypercalciuria is a syndrome of calcium-containing renal stone formation characterized by normocalcaemia, hypophosphataemia and hypercalciuria. Several modalities have been proposed as the primary defect in this disease including intestinal hyperabsorption of calcium, renal "leak" of calcium, renal "leak" of phosphate, hyperparathyroidism, and disturbance of vitamin D metabolism. The oral calcium tolerance test has been used in previous studies to differentiate and investigate the different modalities. Previous reports have suggested that parathyroid hormone may have a role in the pathogenesis of idiopathic hypercalciuria. Recent availability of radioimmunoradiometric assay for intact parathyroid hormone molecule (the main biologically active metabolite) in serum allows the opportunity to further elucidate its involvement in idiopathic hypercalciuria. Parathyroid hormone concentrations where found to be normal in kidney stone forming subjects and the response to calcium loading is normal. However, there is some evidence that a subtle defect in the parathyroid ’set-point’ for calcium is present in stone forming patients. Reports in the literature also suggest there is a defect in the transport of calcium across cell membranes in stone forming subjects. The combination of both these defects would account for the findings in this study. Protein metabolism may have some role in nephrolithiasis and might be more important in hypercalciuric than norrnocalciuric stone forming patients.