Role of 1,25-dihydroxy vitamin D₃ and parathyroid hormone in urinary calcium excretion in calcium stone formers

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.