The role of the sarcopenia index in prognostic assessment of patients with newly initiated peritoneal dialysis: a retrospective cohort study

Background The relationship between the sarcopenia index (SI) and poor prognosis in peritoneal dialysis (PD) is not well established. Methods The SI was calculated using fasting morning serum creatinine (Cr, mg/dL) and cystatin C (CysC, mg/L) levels obtained prior to PD catheter insertion. Two formulas were applied: Cr/CysC and Cr×eGFRcys; eGFRcys was estimated using the Chronic Kidney Disease Epidemiology (CKD-EPI) 2021 equation. Associations between SI and the risk of all-cause mortality or technique failure were analyzed using Cox proportional hazards models and competing risk models. Results In total, 752 PD patients (mean age 42.7 ± 13.4 years; 55.6% men) were included. Multivariate Cox regression showed that both Cr/CysC and Cr×eGFRcys were significantly associated with mortality risk (hazard ratio = 0.476, 95% confidence interval: 0.262–0.866, P = 0.015; hazard ratio = 0.985, 95% confidence interval: 0.973–0.997, P = 0.013, respectively). In the competing risk model, both indices remained independent predictors of mortality. Area under the receiver operating characteristic curve values for predicting mortality were 0.614 for Cr/CysC and 0.669 for Cr×eGFRcys (P < 0.001). No significant association was observed between SI and risk of technique failure. Conclusions Both Cr/CysC and Cr×eGFRcys are independent predictors of mortality in PD patients; Cr×eGFRcys shows superior predictive accuracy.