The association between frailty index and all-cause mortality in US individuals with kidney stones: mediation by systemic immune-inflammation (SII) index

The relationship between the frailty index (FI) and all-cause mortality in patients with kidney stones remains unclear, and whether this relationship is mediated by the systemic Immune-Inflammation index (SII). This cohort study analyzed data from the National Health and Nutrition Examination Survey (NHANES) in the United States, spanning 2007 to 2018. Utilizing Kaplan-Meier survival curves, Cox regression analysis, restricted cubic splines (RCS), and mediation analysis, the research investigated the relationships between FI, SII, and all-cause mortality in individuals with kidney stones. During a median follow-up of 6.3 years (16695 person-years) ,356 total deaths were recorded. A cohort of 2,620 U.S. participants was enrolled from NHANES 2007-2018. Frail individuals demonstrated significantly higher all-cause mortality compared to non-frail counterparts (HR = 1.78, 95% CI: 1.56-2.02, P < 0 0.001). Among patients with kidney stones, the FI showed a positive correlation with the SII (β = 38.18, 95% CI: 10.38-65.99, P < 0.01). The SII indirectly influenced the FI and all-cause mortality in these patients, accounting for 5.6% of the mediating effect. Among U.S. adults with kidney stones, the FI is linked to a higher risk of all-cause mortality, with SII potentially serving as a biological mechanism.