Linear association between the systemic immune-inflammation index and all-cause mortality in patients with interstitial lung disease: a retrospective cohort study.

Objective: To investigate the association between the systemic immune-inflammation index (SII) and all-cause mortality in patients with interstitial lung disease (ILD). Methods: This retrospective cohort study included 366 patients with ILD. SII was calculated using peripheral blood counts and analyzed as both a continuous and categorical variable based on the optimal cutoff value determined by receiver operating characteristic (ROC) analysis. Kaplan-Meier survival curves were used to compare survival between SII groups. Univariable and multivariable Cox proportional hazards models were applied to evaluate the association between SII and all-cause mortality. Restricted cubic spline (RCS) analysis was performed to assess the dose-response relationship. Subgroup analyses were conducted to examine the robustness of the association. Results: Over a median follow-up of 20.6 months, the primary outcome of all-cause mortality occurred in 91 patients (24.9%). The median SII was significantly higher in deceased patients compared with survivors (1471.14 vs. 1017.21). ROC analysis showed a statistically significant discriminatory ability of SII for mortality prediction (AUC = 0.658, 95% CI 0.594-0.723). Kaplan-Meier analysis demonstrated significantly lower survival in patients with high SII (log-rank Conclusion: Elevated SII is independently and linearly associated with increased all-cause mortality in patients with ILD. These findings suggest that SII may have potential clinical value in the assessment and management of patients with ILD.