Association between thyroid hormone sensitivity indices and sarcopenia in patients with chronic kidney disease: a retrospective analysis

Introduction Sarcopenia is a common complication of chronic kidney disease (CKD) and is associated with adverse clinical outcomes. However, the relationship between thyroid hormone sensitivity and sarcopenia in CKD remains unclear. Methods This retrospective study included 252 patients with CKD who were treated between December 2022 and November 2025. According to the Asian Working Group for Sarcopenia 2019 criteria, 80 patients had sarcopenia and 172 did not. Thyroid function parameters measured on the second day of admission were used to calculate the free triiodothyronine/free thyroxine (FT3/FT4) ratio, TSH index (TSHI), thyrotropin-T4 resistance index (TT4RI), and thyroid feedback quartile index (TFQI). Associations between thyroid hormone sensitivity indices and sarcopenia were assessed using correlation analysis, restricted cubic spline (RCS) analysis, multivariable logistic regression, and receiver operating characteristic (ROC) curve analysis. Results The FT3/FT4 ratio was positively correlated with eGFRcr-cys and negatively correlated with urine albumin-to-creatinine ratio (UACR), whereas TSHI and TFQI showed opposite correlations (all P<0.05). After adjustment for sex, age, BMI, serum albumin, eGFRcr-cys, UACR, and hs-CRP, the FT3/FT4 ratio remained inversely associated with sarcopenia (OR = 0.574, P = 0.029), while higher TSHI (OR = 2.340, P = 0.003) and TFQI (OR = 1.183, P = 0.006) were independently associated with greater odds of sarcopenia. RCS analyses showed approximately linear positive associations for TSHI and TFQI and an approximately linear inverse association for FT3/FT4, with no significant evidence of nonlinearity. The AUCs were 0.606 for FT3/FT4, 0.619 for TSHI, 0.714 for TFQI, and 0.813 for their combination; DeLong’s test showed a significantly greater AUC for the combined indices than for each individual index (all P<0.05). Discussion These findings suggest that thyroid hormone sensitivity indices are independently associated with sarcopenia in CKD and may provide complementary discriminative information.