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

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.

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.

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.

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 not applicable.