A Study on the Impact of Concurrent Serum Creatinine/Cystatin C Ratio and Depression on Disability Risk in Chinese Older Adults Using CHARLS Data

Objective To examine the independent effects of the serum creatinine to cystatin C ratio (CCR) and depression on the risk of disability, as well as their interaction, among older adults in China. Methods This study utilized data from the 2015 China Health and Retirement Longitudinal Study (CHARLS) and included 5,192 individuals aged ≥ 60 years. Multivariable logistic regression models were employed to analyze the independent associations of CCR and depression with disability, and multiplicative interaction terms were introduced to evaluate their interaction. Additionally, restricted cubic splines were used to explore the dose-response relationship between CCR and the risk of disability. Results Among all participants, the prevalence of disability was 22.65% (1,176/5,192). After multivariable adjustment, both a low CCR level (OR = 1.20, 95% CI: 1.02–1.42, P = 0.025) and depression (OR = 2.13, 95% CI: 1.84–2.48, P < 0.001) were independent risk factors for disability. Interaction analysis revealed a significant multiplicative interaction effect between CCR and depression (OR = 2.695, 95% CI: 2.150–3.386), indicating that their combined effect on disability risk exceeded the product of their individual independent effects. Restricted cubic spline analysis suggested a nonlinear negative correlation between CCR and the risk of disability (P for nonlinearity = 0.033). Conclusion In the Chinese older adult population, both low-level CCR and depression are significant independent risk factors for disability. Moreover, they exhibit a synergistic interaction, jointly exacerbating the risk of disability. It is recommended that clinical management and public health interventions for disability in older adults adopt integrated strategies that combine muscle function preservation, physical function rehabilitation, and mental health promotion.