Association between the systemic inflammation response index and all-cause mortality in patients with chronic respiratory diseases: A nationwide cohort study from the NHANES 2001–2018

Background Chronic respiratory diseases (CRDs) are leading causes of morbidity and mortality worldwide, yet simple prognostic biomarkers are lacking. The systemic inflammation response index (SIRI) integrates neutrophil, monocyte and lymphocyte counts and has shown prognostic value in malignancies and cardiovascular disease, but its role in CRDs remains unclear. We hypothesized that higher baseline SIRI is independently and dose-dependently associated with increased all-cause mortality across the spectrum of CRDs. Methods We analyzed data from the National Health and Nutrition Examination Survey (NHANES) 2001–2018, including 7923 adults with CRDs (asthma, emphysema or chronic bronchitis). SIRI was calculated from a single baseline complete blood count. Participants were followed until death or 26 April 2022 (median 7.4 years). Cox proportional-hazards models (three levels of adjustment) evaluated the association between SIRI tertiles and all-cause mortality. Sensitivity analyses included continuous SIRI, a clinically derived cut-off (12.98) and CRD-specific sub-cohorts. Results Higher SIRI tertiles were progressively associated with increased mortality: fully-adjusted hazard ratios (Model 3) were 1.19 (95% CI 1.02–1.39) and 1.88 (1.63–2.16) for tertiles two and three versus tertile 1 (P-trend <0.001). Each 1-unit rise in continuous SIRI conferred an 1.01% excess risk (HR 1.0101, 95% CI 1.0082–1.0121). The unitless cut-off value of ≥12.98 identified a high-risk group with an increased risk of all-cause mortality (HR 1.69, 95% CI 1.51–1.89). This association was consistent for all-cause mortality across the asthma (HR 1.83), emphysema (HR 1.70), and chronic bronchitis (HR 1.89) sub-cohorts. Conclusions SIRI is an independent, dose-dependent predictor of all-cause mortality in patients with CRDs, performing robustly across asthma, emphysema and chronic bronchitis. These findings support the use of SIRI as a readily available prognostic tool in CRD management.