Systemic Inflammation Response Index (SIRI) as a Novel Predictor for All-Cause Mortality in Patients with Inflammatory Bowel Disease

Background The global public health burden of inflammatory bowel disease (IBD) is rising steadily. The systemic inflammation response index (SIRI), as a promising indicator reflecting systemic inflammatory status, has unknown predictive value for mortality in IBD patients. This study evaluated SIRI’s predictive capability for all-cause mortality in patients with IBD based on UK Biobank data. Methods Using UK Biobank data, we included 7,060 inflammatory bowel disease participants. SIRI was calculated based on baseline monocyte, neutrophil and lymphocyte counts. Associations and mechanistic pathways were explored via Cox regression, restricted cubic splines, and mediation analyses, after comprehensive covariates adjustment. Results After comprehensive covariate adjustment, elevated SIRI per unit was independently linked to a 5.4% increase in mortality hazard (HR = 1.054, 95% CI: 1.037–1.071). The highest SIRI quartile was associated with a 1.9-fold greater mortality hazard compared with the lowest SIRI quartile. A nonlinear relationship existed (P < 0.001), with risk rising sharply above SIRI 1.24. Handgrip strength, Red blood cell distribution width, and C-reactive protein served as partial mediators underlying this association. Conclusion Elevated systemic inflammation response index is independently linked to higher all-cause mortality in IBD patients in a non-linear manner. Derived from simple routine blood index, SIRI may help identify high-risk patients and guide clinical management.