Systemic immune-inflammation index is associated with adverse outcomes in patients hospitalized for AECOPD: A multicenter cohort study.

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Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are associated with increased morbidity and mortality. The novel inflammatory biomarker, systemic immune-inflammation index (SII), may have prognostic value. This study aimed to assess the association between SII and short-term and long-term adverse outcomes among AECOPD inpatients. This was a multicenter, retrospective analysis of a prospectively collected cohort of AECOPD inpatients. We initially compared SII and other clinical characteristics between survivors and non-survivors during hospitalization, adjusting for primary comorbidities using propensity score matching (PSM). We assessed the short-term and long-term adverse outcomes, particularly focusing on in-hospital mortality and 2-year all-cause mortality, across different levels of SII. Multivariate Cox analysis was employed to evaluate the associations of SII, neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) with in-hospital mortality of AECOPD patients. Restricted cubic spline (RCS) models investigated the nonlinear relationships between these biomarkers and in-hospital mortality. To compare the predictive values of SII, NLR, and PLR for in-hospital mortality, receiver operating characteristic (ROC) curve analysis was performed. Subgroup analysis was carried out to further determine the predictive capacity of SII among diverse subgroups. The study included 12,551 AECOPD inpatients, among whom 180 (1.4%) died in hospital. Whether before or after PSM adjusting for comorbidities, the levels of SII, NLR, and PLR in non-survivors were significantly higher than those in survivors (all P < 0.001). Elevated SII levels (divided into quartiles) were associated with increased in-hospital mortality (Q1 vs. Q2 vs. Q3 vs. Q4: 0.6% vs. 0.8% vs. 1.5% vs. 2.8%) and 2-year all-cause mortality (15.4% vs. 22.6% vs. 22.2% vs. 27.8%), as well as other adverse outcomes (all P < 0.05). After adjusting for covariates, higher levels of SII and NLR consistently remained associated with increased in-hospital mortality. RCS analysis revealed a consistent linear relationship between SII and in-hospital mortality, while NLR and PLR exhibited nonlinear relationships. Furthermore, ROC curve analysis indicated that SII showed inferiority to NLR but superiority to PLR in predicting in-hospital mortality among AECOPD patients (area under the curve for SII vs. NLR vs. PLR: 0.670 vs. 0.731 vs. 0.609). Subgroup analysis revealed that the association between SII and in-hospital mortality varied across different subgroups. Elevated SII is associated with increased risks of short-term and long-term adverse outcomes in AECOPD inpatients, making it potential prognostic factor used to identify high-risk patients and guide the management of AECOPD.