Nonlinear associations of systemic immune-inflammation index with all-cause and cardiovascular mortality in US adults with rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic systemic inflammatory autoimmune disease. However, the relationship between the systemic immune-inflammation index (SII) and the prognosis of RA patients remains unclear. This study aimed to investigate the association between inflammatory biomarker SII and all-cause and cardiovascular mortality in RA patients. A retrospective analysis was conducted using data from the National Health and Nutrition Examination Survey database spanning from 1999 to March 2020. We assessed the association between the SII and all-cause as well as cardiovascular mortality in RA patients employing multivariable Cox proportional hazards regression analysis and restricted cubic spline plots. Receiver operating characteristic curves were employed to evaluate the prognostic capacity of SII in predicting outcomes in both the RA patients and the general population, alongside its predictive performance compared to other markers. This study comprised 2247 RA patients and a control cohort of 29,177 individuals from the general population. Over a 20-year follow-up period, 738 all-cause deaths and 215 deaths attributable to cardiovascular disease were documented in RA patients. We observed a nonlinear positive correlation between the SII and both all-cause and cardiovascular mortality in RA patients. Of significance, at an SII level of 529.7, the hazard ratio reached 1, signifying a transition from low to high mortality risk. Moreover, subgroup analysis did not reveal any potential interactions. Our study findings indicate a nonlinear positive correlation between the inflammatory biomarker SII and both all-cause and cardiovascular mortality in patients with RA.