Higher serum phosphorus predicts residual renal function loss in male but not female incident peritoneal dialysis patients

Background Elevated serum phosphorus level is a risk factor for progression of chronic kidney disease in non-dialysis patients. However, the association of serum phosphorus level with residual renal function (RRF) loss among incident continuous ambulatory peritoneal dialysis (CAPD) patients remains unclear. Methods We performed a retrospective analysis of prospectively collected cohort of 1245 incident CAPD patients from January 2006 to December 2015 and followed up until December 2017. Patients were stratified into tertiles according to baseline serum phosphorus levels. RRF loss was defined as residual glomerular filtration rate (mL/min/1.73 m(2)) reaching zero or estimated urine output less than 200 mL/day on two successive clinic visits. Propensity-score matched Cox's proportional hazards and competing risk models were performed to examine the association of serum phosphorus with RRF loss. Results A total of 421 (33.82%) patients had loss of RRF over a median follow-up of 26.23 months. In the entire cohort, elevated serum phosphorus was associated with increased risk for RRF loss after adjustment. In the propensity-score matched cohort, patients in the 3rd tertile of serum phosphorus had a 51% higher risk of RRF loss than those in the combination of the 1st and 2nd tertiles. Furthermore, the association of serum phosphorus level with RRF loss differed by sex (interactionP = 0.018). The adjusted HRs per 1 mg/dL increase in serum phosphorus level of RRF loss were 1.32 (95% CI 1.15-1.50,P < 0.001) for male and 1.03 (95% CI 0.87-1.21,P = 0.750) for female, respectively. These findings persisted in competing risk analysis. Conclusion Higher serum phosphorus levels independently predicts RRF loss in men treated with CAPD.