Supplementary Material for: High Intraperitoneal Interleukin-6 Levels Predict Peritonitis in Peritoneal Dialysis Patients: A Prospective Cohort Study

<b><i>Background:</i></b> To evaluate the predictive value of dialysate interleukin-6 (IL-6) representing local subclinical intraperitoneal inflammation for the development of peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients. <b><i>Methods:</i></b> Stable prevalent CAPD patients were enrolled in this prospective study. IL-6 concentration in the overnight effluent was determined and expressed as the IL-6 appearance rate (IL-6AR). Patients were divided into 2 groups according to the median of IL-6AR and prospectively followed up until the first episode of peritonitis, cessation of PD, or the end of the study (December 30, 2017). The utility of IL-6AR in predicting peritonitis-free survival was analyzed using the Kaplan-Meier and Cox proportional hazards models. <b><i>Results:</i></b> A total of 149 patients were enrolled, including 72 males (48%) with mean age 52.0 ± 13.6 years and median PD duration 26 (5.9–45.5) months. During follow-up, 7,923 patient months were observed and 154 episodes of peritonitis occurred in 82 patients. Previous peritonitis episodes were significantly associated with log dialysate IL-6AR levels (β = 0.187 [0.022–0.299], <i>p</i> = 0.023). Patients in the high IL-6AR group showed a significantly inferior peritonitis-free survival when compared with their counterparts in the low IL-6AR group (48.8 vs. 67.7 months, <i>p</i> = 0.026), as well as higher treatment failure percentage of peritonitis (20.3 vs. 9.3%, <i>p</i> = 0.049). A multivariate Cox regression showed that high dialysate IL-6AR (hazard ratio [HR] 1.247 [1.052–1.478]; <i>p</i> = 0.011) and high serum C-reactive protein (HR 1.072 [1.005–1.144]; <i>p</i> = 0.036) were independent risk factors for inferior peritonitis-free survival. <b><i>Conclusion:</i></b> This prospective study suggested that the intraperitoneal inflammation marker, dialysate IL-6 level, might be a potential predictor of peritonitis development in patients undergoing PD.