Elevated SII is significantly associated with increased COPD risk, all-cause mortality, and respiratory failureInflammation Markers Linked to Higher Risk of Respiratory Failure

BackgroundRecent evidence suggests that Systemic Immune-Inflammation Index (SII) and Systemic Inflammatory Response Index (SIRI) are associated with the presence and prognosis of patients with chronic obstructive pulmonary disease (COPD). However, existing research results remain controversial.MethodsPubMed, Embase, Web of Science, and the Cochrane Library were systematically searched from inception to March 23, 2026. Observational studies investigating the associations of SII or SIRI with COPD risk, all-cause mortality (ACM), or respiratory failure (RF) were included. Data were analyzed using Review Manager 5.4.1 and Stata 15.1. Heterogeneity was assessed using Cochran’s Q test and the I2 statistic, with subgroup analyses conducted when substantial heterogeneity was detected. Sensitivity analyses were performed using a leave-one-out approach to evaluate the robustness of the findings. Publication bias was assessed through funnel plots and Egger’s regression test. A two-sided p < 0.05 was considered statistically significant.ResultsEleven studies involving 59,621 participants were included. Elevated SII was significantly associated with the higher prevalence of COPD (OR = 1.22, 95% CI: 1.06–1.41), higher ACM (OR = 1.20, 95% CI: 1.09–1.36), and an higher risk of RF (OR = 1.61, 95% CI: 1.28–2.02). In contrast, no significant association was observed between SIRI and COPD risk (OR = 1.14, 95% CI: 0.90–1.45). Subgroup analyses indicated that the association between SII and COPD risk was not statistically significant in cohort studies, populations aged ≥65, studies conducted in Europe, and patients with acute exacerbations of COPD (AECOPD). Sensitivity analyses confirmed the stability of the pooled estimates, and no significant publication bias was detected by funnel plots or Egger’s test.ConclusionCompared with SIRI, SII is an easily measurable and promising biomarker. Existing evidence confirms its association with COPD prevalence, ACM, and RF. Further prospective studies shall establish standardized cutoff values and validate their clinical utility across diverse populations.