The trajectory of frailty index and its association with rapid decline in kidney function and the incidence of chronic kidney disease: evidence from the China health and retirement longitudinal study.

Background: This study aims to evaluate the association between the frailty index trajectory in older adults from a longitudinal cohort and rapid decline in kidney function as well as the incidence of chronic kidney disease (CKD).

Method: This study included 4,207 participants aged 45 and above from the China Health and Retirement Longitudinal Study (CHARLS), who underwent baseline assessments in 2011-2012 and were followed up in 2013 and 2015. The study selected 31 items to construct the frailty index (FI), with the FI value positively correlated with the degree of frailty in individuals. The FI trajectories were determined using latent class trajectory modeling (LCTM). The primary outcome event was rapid decline in kidney function, with the incidence of CKD also being explored. Binary logistic regression analysis was used to examine the association between these trajectories and kidney disease. The covariates include basic demographic variables, medical history, and biochemical indicators. In addition, the dose-response relationship between cumulative frailty indicators and rapid decline in kidney function and CKD was explored within each frailty index trajectory group. We conducted subgroup and interaction analyses to explore the impact of various characteristics on this relationship. Finally, eGFRcr was used to assess kidney function and validate the consistency of previous findings.

Results: Participants were divided into three FI trajectories: Low-stable trajectory, Moderate-stable frailty index trajectory, and Moderate-increase trajectory, which accounted for 50.68%, 37.58%, and 11.74% of the study population, respectively. Compared to participants in the Low-stable frailty index trajectory group, those in the Moderate-increase FI trajectory group had a significantly higher risk of rapid decline in kidney function, with an adjusted OR of 1.589 (95% CI, 1.013-2.442). However, the trend ORs for cumulative FI within each FI group did not show statistical significance, suggesting the reasonableness of the trajectory classification. Finally, the analysis using eGFRcr to assess kidney function was consistent with the primary results.

Conclusion: A higher FI trajectory is associated with an increased risk of rapid decline in kidney function. The findings underscore the critical importance of monitoring the dynamic changes in frailty among middle-aged and older adults.