Association between cumulative changes of the C-reactive protein-triglyceride glucose index and the incidence of rapid kidney function decline: a nationwide prospective cohort study

Background: Rapid kidney function decline (RKFD) is an early indicator of chronic kidney disease and a precursor to kidney failure, yet early detection is challenging. Inflammation and metabolic imbalance may cause kidney damage, and the C-reactive protein-triglyceride glucose index (CTI) represents both factors. This study aims to explore the associations of cumulative changes of CTI (cuCTI) with RKFD risk in middle-aged and older adults. Methods: We analyzed data from 6,888 individuals aged 45 and older from the 2011 and 2015 China Health and Retirement Longitudinal Study (CHARLS). Using multivariate logistic regression models, we explored the association between cuCTI, CTI control levels, and RKFD risk. We also used restricted cubic spline (RCS) models for dose-response patterns and conducted subgroup analyses based on sex, education, smoking, alcohol use, hypertension, diabetes, dyslipidemia, and CKD stage. Sensitivity analyses were performed on original, imputed, and pooled datasets to ensure robust results. A supplementary cross-sectional analysis using National Health and Nutrition Examination Survey analysis (NHANES) data examined the association between CTI and eGFR using weighted linear regression and RCS models. Results: Over a four-year period, 262 participants (3.8%) developed RKFD. Increased cuCTI and poor CTI control were linked to a higher RKFD risk, with each one-unit cuCTI increase raising the odds by 18% (OR = 1.18, 95% CI: 1.13-1.22). Those with consistently high or rising CTI faced the greatest risk. The dose-response curve indicated a linear increase in RKFD risk with higher cuCTI, and subgroup analyses showed consistent results across all groups. Sensitivity analyses confirmed the stability of these associations across datasets. Similar associations were observed in the supplementary analysis using NHANES data, with higher CTI levels associated with lower eGFR. Conclusion: Higher cumulative CTI levels were associated with an increased risk of rapid kidney function decline, and the association was most pronounced among individuals with persistently high CTI levels. Monitoring long-term inflammatory and metabolic status may help identify individuals at risk of renal function decline in middle-aged and older adults.