Abstract
<title>Abstract</title> <p> Background Sarcopenia index (SI) and creatinine-to-cystatin C ratio (CCR) are established serologic surrogates of sarcopenia that correlate with all-cause mortality in the general geriatric population. However, their prognostic value remains uncertain in individuals with ADL disability, a demographic characterized by exceptionally high mortality risk. This study sought to examine the association between SI, CCR, and all-cause mortality in individuals with ADL disability. Methods This prospective cohort study followed 1,421 older adults with daily living activity impairments from the China Health and Retirement Longitudinal Study (CHARLS) project, with death as the primary outcome. Associations were examined using Cox proportional hazards models, restricted cubic splines, and threshold effect models. The robustness of the results was subsequently evaluated through sensitivity and subgroup analyses. Results In the fully adjusted model, elevated SI and CCR levels predicted a marked reduction in all-cause mortality risk. Compared with the lowest quartile, the risk ratios for mortality were 0.62 for SI (95%CI, 0.45–0.84; <italic>P</italic> < 0.002) and 0.58 for CCR (95%CI, 0.43–0.79; <italic>P</italic> < 0.001). Threshold analysis revealed that below the inflection points (CCR = 0.68, SI = 66.31), increases in either marker significantly lowered mortality risk; above those points, the protective association weakened. Subgroup and multiple sensitivity analyses confirmed the robustness of these findings. Conclusions For middle-aged and older adults living in the community who have trouble with ADL, SI and CCR both turned out to be important predictors of a lower risk of all-cause mortality, and the relationship is non-linear. We recommend these markers should be used in primary care to help identify high-risk individuals for more targeted management. </p>