Association of systemic immune-inflammation index with the risk of incident pre-frailty or frailty: the Chinese Longitudinal Healthy Longevity Survey

Abstract

Background: Inflammation is a significant factor in the pathogenesis of frailty. While previous research has indicated that the systemic immune-inflammation index (SII) serves as a reliable marker for inflammation, the relationship between SII and newly developed frailty remains understudied. This study aims to explore the relationship between SII and incident pre-frailty and frailty among community-dwelling older adults. Methods: Data were drawn from participants in the 2008 wave of the Chinese Longitudinal Healthy Longevity Survey (CLHLS). A 38-item frailty index (FI) was employed to assess frailty status and to classify participants into one of three categories: “robust” (FI ≤ 0.1), “pre-frail” (0.1 < FI ≤ 0.21), or “frail” (FI > 0.21). The SII was determined using the formula: SII = (white blood cell – lymphocyte) × (platelet count) / lymphocyte. A Cox regression model was utilized to evaluate the relationship between SII and the onset of pre-frailty and frailty. Results: The analysis included 676 participants classified as robust, with a median age of 80.0 years (interquartile range, 67.0, 91.0). Over a 3-year follow-up period, 159 participants progressed to a state of pre-frailty or frailty. The incidence of pre-frailty or frailty was 17.8%, 25.3%, and 27.6% across SII tertile groups, respectively (p < 0.05). Among participants initially categorized as robust in 2008, those in the highest SII tertile had a greater risk of developing pre-frailty or frailty compared to those in the lowest tertile (HR = 2.03; 95% CI: 1.12–3.70). Sensitivity analysis using the Fine-Gray model, accounting for death as a competing risk, also indicated an elevated risk for those in the highest SII tertile (HR = 1.53; 95% CI: 1.18–1.98). Conclusion: Among community-dwelling older adults, higher SII levels were associated with an increased risk of incident pre-frailty or frailty.