Abstract: Objective  To investigate the early predictive value of the systemic immune-inflammation index (SII) for the first episode of peritoneal dialysis-associated peritonitis (PDAP) in patients undergoing peritoneal dialysis (PD). Methods  PD patients treated in the Department of Nephrology at the First Affiliated Hospital of Chengdu Medical College from November 2010 to November 2023 were selected. Based on the occurrence of the first PDAP, patients were divided into a peritonitis group and a non-peritonitis group. Correlation analysis and Logistic regression were used to study the relationship between SII and the first PDAP, and receiver operating characteristic (ROC) curves were plotted to analyze the predictive value of SII for the first PDAP. Results A total of 302 patients were included, with 137 in the peritonitis group and 165 in the non-peritonitis group. Compared to the non-peritonitis group, the peritonitis group had longer dialysis vintage, higher SII values, neutrophil counts, monocyte counts, and higher low-density lipoprotein cholesterol levels (Z=-4.641, -5.221, -7.446, -2.114, -2.305; P ＜0.001, ＜0.001, ＜0.001, 0.034, 0.021). Correlation analysis showed a positive correlation between SII levels and the first PDAP (r = 0.231, P＜0.001). Multivariate Logistic regression analysis indicated that a high SII (OR = 1.001, 95% CI: 1.000～1.001, P＜0.001) and longer dialysis vintage (OR = 1.020, 95% CI: 1.011～1.029, P ＜0.001) were independent risk factors for the first PDAP. The ROC curve showed that the area under the curve (AUC) for SII in predicting the first PDAP was 0.674 (95% CI: 0.615～0.734), with an optimal cut-off value of 780.51, sensitivity of 70.8%, and specificity of 58.2%.  Conclusion  Elevated SII and  longer dialysis  vintage are independent risk factors for first episode PDAP, and SII can serve as an early predictive marker.

Key words: Systemic immune-inflammation index, Peritoneal dialysis, Peritoneal dialysis-associated peritonitis, Predictive value