The relationship of Systemic Inflammatory Index with asthma in adults: A retrospective cross-sectional study

Backgrounds The Systemic Inflammatory Index, a comprehensive marker of blood inflammation linked to multiple diseases, was examined for its association with adult asthma in this large-scale study. Methods We analyzed data from the National Health and Nutrition Examination Survey (2009–2020) to explore the relationship between adult asthma (defined by self-report/medication use) and the Systemic Inflammatory Index score (calculated using blood cell counts). We employed weighted logistic regression analysis and restricted cubic splines to examine associations and nonlinear relationships. Subgroup analyses were conducted to evaluate potential interactions among subgroups stratified by sex, age, race, educational level, poverty–income ratio, smoking status, and alcohol consumption. Results There were 23,176 participants in this study; of these, 3840 (15.02%) had asthma. Logistic regression analysis showed that high Systemic Inflammatory Index (log 2 -transformed) scores were associated with increased asthma prevalence. Subgroup analysis revealed that there is no significant interaction effects in the association between the two entities across subgroups ( p for interaction >0.05). Restricted cubic spline plots showed a consistent upward trend in asthma prevalence with increasing Systemic Inflammatory Index scores. Conclusions Overall, higher Systemic Inflammatory Index scores were associated with higher prevalence of adult asthma in this study. As a cost-effective and readily accessible composite inflammatory marker, the Systemic Inflammatory Index holds potential clinical value in the diagnosis and prevention of adult asthma.