Relationship between systemic immune-inflammation index and long-term all-cause and cause-specific mortality among adult asthma patients: a population-based study

Background: Persistent inflammation in the airways is a hallmark of asthma, and researchers have extensively explored various inflammatory indicators that contribute to the condition. Despite this, there is limited research on the relationship between the systemic immune-inflammation index (SII), a novel marker of inflammation, and overall mortality rates as well as mortality rates due to specific causes in individuals with asthma.

Methods: We analyzed data from the National Health and Nutrition Examination Survey (NHANES) covering a 20-year period, from 1999 to 2018. To examine the association between SII and mortality rates in asthma patients, we used a combination of statistical methods, including weighted Kaplan-Meier analysis and multivariate-adjusted Cox analysis. Additionally, we applied restricted cubic spline (RCS) analysis to investigate the potential non-linear relationship between these variables. To further validate our findings, we performed subgroup and sensitivity analyses to ensure the reliability of the results.

Results: This study analyzed data from 5,384 individuals with asthma, finding a link between increased SII levels and a higher risk of death from all-cause, cardiovascular disease and respiratory disease, but no association with cancer mortality. There were J-shaped non-linear relationships between SII and all-cause, cardiovascular and respiratory diseases mortality in asthma patients. The inflection points were 326, 350 and 355, respectively. Below these inflection points, each 100-unit increase in SII was associated with a decrease in mortality by 8%, 11% and 10%, while above these thresholds, mortality rates increased by 4%, 4%, and 3%, respectively. Subgroup analyses showed that SII was a significant predictor of all-cause mortality across various subgroups, and sensitivity analyses confirmed these findings, with the highest SII group consistently showing higher mortality rates for all-cause, cardiovascular, and respiratory disease mortality in the fully adjusted model.

Conclusions: Our study initially demonstrated a strong link between elevated SII levels and a higher risk of death from all-cause, cardiovascular disease, and respiratory disease in individuals with asthma. Furthermore, our analysis showed that the relationship between SII and mortality rates in asthma patients followed a non-linear, J-shaped pattern for all-cause, cardiovascular, and respiratory disease mortality.

Clinical trial number: Clinical trial number not applicable.