The effects of dialysate calcium prescription on mortality outcomes in incident patients on hemodialysis

Background The appropriate prescription of dialysate calcium concentration for hemodialysis is debated. We investigated the association between dialysate calcium and all-cause, cardiovascular mortality and sudden cardiac death.Methods In this historical cohort study, we included adult incident hemodialysis patients who initiated dialysis between 1 January 2010 and 30 June 2017 who survived for at least 6 months (grace period). We evaluated the association between dialysate calcium 1.25 or 1.50 mmol/l and outcomes in the 2 years after the grace period, using multivariable Cox regression models. Moreover, we examined the association between the serum dialysate to calcium gradient and outcomes.Results We included 12 897 patients with dialysate calcium 1.25 mmol/l and 26 989 patients with dialysate calcium 1.50 mmol/l. The median age was 65 years, and 61% were male. The unadjusted risk of all-cause mortality was higher for dialysate calcium 1.50 mmol/l [hazard ratio (HR) 1.07, 95% confidence intervals (CI) 1.01-1.12]. However, in the fully adjusted model, no significant differences were noted (HR 1.05, 95% CI 0.99-1.12). Similar results were observed for the risk of cardiovascular mortality (HR 1.03, 95% CI 0.94-1.13). Adjusted risk of sudden cardiac death was lower for dialysate calcium 1.50 mmol/l (HR 0.81, 95% CI 0.67-0.97). Significant and positive associations with all outcomes were observed with larger serum-to-dialysate calcium gradients, primarily mediated by the serum calcium level.Conclusions In contrast to the unadjusted analysis that showed a higher risk for dialysate calcium of 1.50 mmol/l, after adjusting for confounders, there were no significant differences in the risk of all-cause and cardiovascular mortality between dialysate calcium concentrations of 1.50 and 1.25 mmol/l. After adjustment, a lower risk of sudden cardiac death was observed in patients with dialysate calcium 1.50 mmol/l. A higher serum-to-dialysate calcium gradient is associated with an increased risk for adverse outcomes. Graphical Abstract