Abstract: Objective This study aimed to evaluate the predictive value of combining the Prognostic Nutritional Index (PNI) and the Systemic Immune-Inflammation Index (SII) for all-cause mortality in patients undergoing peritoneal dialysis (PD). Methods PD patients diagnosed and treated in the Department of Nephrology at the Second Xiangya Hospital of Central South University between June 1, 2014, and May 31, 2024, were enrolled. Receiver operating characteristic (ROC) curve analysis determined optimal cut-off values for PNI and SII. Patients were divided into four groups based on these cut-offs: Group A (High PNI / Low SII), Group B (High PNI / High SII), Group C (Low PNI / Low SII), and Group D (Low PNI / High SII). Baseline characteristics were compared across groups. Kaplan-Meier (K-M) analysis was performed to assess differences in survival rates. Cox proportional hazards regression models evaluated the impact of PNI, SII, and PNI-SII on all-cause mortality. ROC curves and decision curve analysis were used to evaluate predictive performance and clinical utility. Results A total of 955 patients were included. The cut- off values for PNI and SII were 40.875 and 691.954, respectively. Groups A, B, C, and D comprised 275, 282, 199, and 199 patients, respectively. Kaplan-Meier curves demonstrated a statistically significant difference in the cumulative all-cause mortality risk among groups (log-rank test χ2 =116.000, P＜0.001). After adjusting for key confounding factors, Group D had a 7.6- fold increased risk of all-cause mortality compared to Group A (95% Confidence Interval [CI]: 2.08～27.64, P=0.002). The area under the curve (AUC) for PNI- SII in predicting allcause mortality was 0.822 (95% CI: 0.780～0.864), surpassing that of PNI alone (0.777, 95% CI: 0.732～0.821; DeLong test Z= 4.755, corrected P＜0.001) and SII alone (0.692, 95% CI: 0.639～0.745; DeLong test Z=14.277, corrected P＜0.001). Conclusion The combination of PNI and SII offers superior predictive accuracy and greater clinical utility for all-cause mortality risk stratification in PD patients compared to either in dex used alone.

Key words: Prognostic nutritional index, Systemic immune- inflammation index, Peritoneal dialysis, All-cause mortality