Serum Creatinine/Cystatin C-Based Muscle Indices for Sarcopenia and Graft Failure After Living Donor Liver Transplantation.

Background/Objectives: Sarcopenia adversely affects outcomes after liver transplantation. The CT-based skeletal muscle index (SMI) is a validated prognostic measure but requires dedicated image analysis. We evaluated the diagnostic performance of creatinine/cystatin C-based serum muscle indices for identifying CT-defined sarcopenia and their prognostic value for graft failure in living donor liver transplantation (LDLT) recipients. Methods: We retrospectively analyzed 802 LDLT recipients (January 2023-April 2026). Using serum creatinine- and cystatin C-based equations, we calculated total body muscle mass (TBMM), appendicular skeletal muscle mass (ASM), and predicted SMI, and derived height-squared-normalized indices (TBMMI, ASMI); the creatinine-to-cystatin C ratio served as a non-equation-based comparator. CT-defined sarcopenia was classified using sex-specific reference cutoffs (males < 39.9, females < 28.9 cm2/m2). Diagnostic accuracy was assessed with sex-stratified ROC curves and DeLong test. The primary outcome was graft failure (recipient death or re-transplantation); its association with the best-performing index at 180 days, 1 year, and 3 years was evaluated using multivariable Cox models. Results: TBMMI showed the strongest correlation with SMI (r = 0.75). TBMMI discriminated CT-defined sarcopenia well (AUC 0.845 in males, 0.828 in females). After multivariable adjustment, each 1 kg/m2 decrease in TBMMI was independently associated with graft failure at 180 days (adjusted hazard ratio [HR] 1.42, 95% CI, 1.14-1.78), 1 year (HR 1.28, 1.05-1.56), and 3 years (HR 1.20, 1.02-1.40) (all p < 0.05). Conclusions: TBMMI is an accessible, non-imaging surrogate for SMI in LDLT recipients, and a lower TBMMI is independently associated with postoperative graft failure.