Association Between Serum Creatinine to Cystatin C Ratio and Activities of Daily Living Disability Trajectories: Evidence From the China Health and Retirement Longitudinal Study

INTRODUCTION: The severity of activities of daily living (ADL) disability, encompassing basic activities of daily living (BADL) disability and instrumental activities of daily living (IADL) disability, exhibited dynamic changes and heterogeneity across individuals. Serum creatinine to cystatin C ratio (CCR) was identified as a predictor of sarcopenia. This study aimed to clarify the ADL/BADL/IADL disability trajectories and their relationships with the CCR among Chinese middle-aged and older people. METHODS: The study included 4617 participants from the China Health and Retirement Longitudinal Study. Group-Based Trajectory Modeling (GBTM) was applied to explore the ADL/BADL/IADL disability trajectories. Using logistic regression analysis to estimate the associations between CCR and these trajectories. RESULTS: Three ADL/BADL/IADL disability trajectories were identified: low-level stable group, low-level increasing group, and high-level increasing group. Logistic analysis showed that higher CCR was significantly associated with lower odds of being classified into group 2 (OR = 0.91, 95% CI = 0.88-0.95) and group 3 (OR = 0.85, 95% CI = 0.79-0.92) in ADL. Each one-unit increase in CCR was correlated with 7% and 16% lower odds for BADL group 2 (OR = 0.93, 95% CI = 0.89-0.96) and group 3 (OR = 0.84, 95% CI = 0.78-0.90), 6% (OR = 0.94, 95% CI = 0.90-0.97) and 15% (OR = 0.85, 95% CI = 0.79-0.91) lower odds for IADL group 2 and 3. Interaction analysis demonstrated that CCR, age, marital status, smoking status, hypertension, dyslipidemia, and BMI exhibited significant interactions in their effects on ADL/BADL/IADL disability trajectories. CONCLUSION: Three ADL/BADL/IADL disability trajectories were identified among Chinese middle-aged and older adults. The negative associations were observed between CCR and ADL/BADL/IADL disability trajectories, highlighting the need for targeted strategies.