Systemic Immune-Inflammation Index as a Predictor of Severity and Acute Kidney Injury in Acute Pancreatitis: A Meta-Analysis

Background Early and accurate prediction of disease severity in acute pancreatitis (AP) is critical for guiding timely clinical interventions and improving patient prognosis. The systemic immune–inflammation index (SII), an integrated inflammatory marker derived from neutrophil, lymphocyte, and platelet counts, has demonstrated prognostic value in a variety of diseases. However, its application in AP has not been systematically evaluated. Methods A systematic search was conducted across databases to screen observational studies published up to December 2025 on the correlation between SII and AP. Statistical analysis was performed using R software to calculate the pooled mean difference (MD), odds ratio (OR), as well as pooled sensitivity and specificity of SII as an predictor of severity and poor prognosis of the disease. Results A total of 16 high-quality studies (with NOS scores ranging from 7 to 9) were included, encompassing a total of 3,482 patients. The meta-analysis results indicated that the SII was significantly higher in SAP than non-SAP patients (MD = 1235.79, 95% CI: 847.55–1624.04, P < 0.001). The pooled logistic regression results suggested that elevated SII was an independent risk factor for SAP (OR = 1.001, 95% CI: 1.000–1.002, P = 0.012). The pooled sensitivity, specificity, and AUC of SII for predicting SAP were 0.692 (95% CI: 0.574–0.790), 0.755 (95% CI: 0.616–0.855), and 0.69, respectively. Furthermore, elevated SII were significantly associated with AKI in AP (MD = 1938.81, P < 0.001), but did not show statistical significance in predicting mortality (OR = 2.118, P = 0.133). Despite significant heterogeneity among studies (I ²  = 97.8%) and detection of publication bias (Egger’s test P = 0.0459), sensitivity analysis confirmed the stability of the main results. Conclusion SII is a simple and effective early biomarker for predicting the severity of acute pancreatitis and its concurrent acute kidney injury, demonstrating favorable specificity. Despite being limited by study heterogeneity and potential publication bias, SII still holds potential as an auxiliary tool for early clinical risk stratification.