Renal threshold phosphate concentration in patients with idiopathic nephrolithiasis: correlations with tubular functions, serum parathyroid hormone and 1,25(OH)2D3.

The renal handling of inorganic phosphate was measured in 17 idiopathic nephrolithiasis patients with normal glomerular filtration rate and effective renal plasma flow. TmPO4/GFR was less than 2.5 mg/dl in nine subjects (Group I) and greater than or equal to 2.5 in eight (Group II). The former had serum PO4 of 2.5 +/- 0.13 mg/dl and the latter, 3.5 +/- 0.11 mg/dl (p less than 0.01). Four in Group I and five in Group II were hypercalciuric. There was no significant difference in the serum parathyroid hormone and 1,25(OH)2D3 between the two groups. However, renal tubular functions were abnormal in both groups. The low TmPO4/GFR in 53 per cent of the patients is another manifestation of tubular functional abnormality seen in idiopathic nephrolithiasis.