Association of the systemic immune-inflammation index with all-cause mortality in patients with arteriosclerotic cardiovascular disease

OBJECTIVE: Systemic immune-inflammation index (SII), derived from blood cell counts of circulating platelets, neutrophils, and lymphocytes, has been identified as a novel inflammatory and prognostic marker. However, the clinical value of SII in patients with arteriosclerotic cardiovascular disease (ASCVD) had not been further explored. Thus, this study is designed to explore the associations of SII with mortality in ASCVD individuals. METHODS: All individuals with ASCVD aged ≥20 years were included from the National Health and Nutritional Examination Surveys (NHANES) 2005–2014 and followed for survival until 31 December 2019. Multivariable Cox analysis investigated the associations between SII, evaluated as a continuous variable with splines, as categorical ones (quartiles), and the all-cause death. To demonstrate the association between SII and mortality, subgroup analysis, restricted cubic spline along with piecewise linear regression were also conducted. RESULTS: A total of 2,595 participants (57.8% men) were included. During a median of 7.7 years of follow-up, 1,122 deaths due to all-cause were recorded. After adjusting for multiple confounders, when compared with the patients in quartile 1 (SII ln transform), those in quartile 4 had a 46% increased risk for all-cause death [hazard ratio (HR) = 1.46, 95% confidence interval (CI) = 1.22–1.75]. As a continuous variable, each unit of raised ln-SII was associated with a 24% increased risk of all-cause death (HR = 1.24, 95% CI = 1.10–1.38). In the restricted cubic spline regression model, the relationship between ln-SII and all-cause death was non-linear. The cutoff value of ln-SII for mortality was 6.57 and those with a higher than the threshold point had a 1.25-fold risk of mortality. No significant difference was noted below the threshold points. CONCLUSION: An association was detected between the baseline ln-SII and all-cause mortality in a United States ASCVD population. Increased SII is associated with poor survival in individuals with ASCVD.