Prognostic associations of serum calcium, phosphate and calcium phosphate concentration product with outcomes in kidney transplant recipients

Abstract

Disturbances in calcium and phosphate metabolism have been linked to increased mortality in hemodialysis patients, but not in kidney transplant recipients (KTR). We enrolled 733 KTR from the Vienna General Hospital into this study. Detailed demographic, clinical, laboratory, and transplant-related information was collected at baseline. We used the Austrian Dialysis and Transplantation Registry for follow-up. Using multivariate proportional hazard regression, we examined the independent associations between serum calcium, serum phosphate, and calcium phosphate (CaPO(4)) product with the outcomes of death from any cause and kidney allograft loss. Over a median follow-up of >6 years, 154 patients died and 259 kidney allografts were lost. Associations with serum calcium, phosphate concentrations, and CaPO(4) product concentrations were found for allograft loss, but not for patient mortality. Patients in the highest quintile of phosphate concentration and CaPO(4) product had an increased risk for allograft loss compared with patients in the lowest quintile of these parameters (hazards ratio, HR = 2.15; 95% confidence interval, CI: 1.36-3.40 and HR = 1.72; 95% CI: 1.10-2.71, respectively). High calcium levels were associated with a reduced risk for allograft loss. Results were even more pronounced for death-censored allograft loss. High concentrations of serum phosphate and CaPO(4) product were associated with an increased risk for allograft loss in these KTR, whereas high serum calcium concentrations seemed to lower the risk.