Purpose: To find out the possible role of 1,25(OH)2 vitamin D3 [1,25(OH)2D3] and parathyroid hormone (PTH) as intrinsic factors in urinary calcium stone formers (SFs), we investigated their relationship with serum and urinary biochemical parameters. Materials and Methods: A total of 326 calcium SFs (male: 204, female: 122) were enrolled and underwent outpatient metabolic evaluations including 1,25(OH)2D3 and PTH as well as serum and 24-hour urinary biochemical parameters. As control, 163 age- and sex-matched (2:1) individuals (non-SFs) who have never urinary stone episode were included. Results: 1,25(OH)2D3 level was positively correlated with urinary calcium excretion (r=0.347, p<0.001). The hypercalciuric group and recurrent SFs had higher serum 1,25(OH)2D3 levels than the normocalciuric group (p<0.001) and first SFs (p=0.050). In the adjusted multiple linear regression analysis, serum 1,25(OH)2D3 level (β=0.259, p<0.001) and serum PTH level (β=-0.160, p<0.001) were significantly correlated with urinary calcium excretion. The patients in highest tertile of 1,25(OH)2D3 had a more than 3.1 fold risk of hypercalciuria than those in the lowest tertile (odds ratio=3.14, 95% confidence interval: 1.431-6.888, p=0.004). No correlation was observed between PTH and 1,25(OH)2D3 (R=0.005, p=0.929) in calcium SFs, while a negative correlation was found in controls (R=-0.269, p=0.001). Conclusion: 1,25(OH)2D3 was closely correlated with urinary calcium excretion, and high 1,25(OH)2D3 levels were detected in the hypercalciuric group and in recurrent SFs. However, 1,25(OH)2D3 was not correlated with PTH in calcium SFs. These findings suggest that 1,25(OH)2D3 might be important intrinsic factor for altered calcium regulation in SFs.
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