Triglyceride–Glucose Index as a Predictor of Chronic Kidney Injury in Primary Hypothyroidism: A Retrospective Cohort Study

Introduction: Primary hypothyroidism is a common endocrine disorder, and recent studies have shown a complex relationship between it and chronic kidney disease (CKD). The triglyceride–glucose (TyG) index, a novel metabolic marker, may have significant value in predicting CKD risk in patients with hypothyroidism. This study aims to evaluate the association between the TyG index and CKD risk in this population. Materials and Methods: This retrospective cohort study included 2658 primary hypothyroidism patients from the Lejiu database of Dongyang Hospital. Basic demographic characteristics and clinical laboratory data were collected, and the TyG index was calculated. The association between the TyG index and CKD risk was explored using Cox proportional hazards regression models, Kaplan–Meier survival analysis, and mediation analysis. Results: Among the 2658 patients, the prevalence of CKD was 18.06%. Kaplan–Meier survival analysis revealed a significantly higher incidence of CKD in patients with the highest TyG quartile compared to the lowest (log‐rank test, p = 0.014). Multivariable Cox regression analysis showed that, although the overall hazard ratio (HR) did not reach significance in Model 3, after adjusting for multiple covariates, patients in the TyG Q4 group had a significantly increased risk of CKD compared to the Q1 group (HR = 1.40, 95% CI: 1.06–1.85, p = 0.017). Restricted cubic spline analysis further confirmed a significant nonlinear association between the TyG index and CKD risk, particularly prominent in females ( p ‐nonlinear = 0.01). Subgroup analysis indicated that the TyG index was more strongly associated with CKD risk in females, overweight individuals, and those with hyperlipidemia, anemia, or malnutrition. Mediation analysis revealed that diabetes mellitus had the largest indirect effect, accounting for 76.76% of the total effect, followed by hypertension (70.52%) and systolic blood pressure (64.42%), with all indirect effects reaching statistical significance ( p < 0.05). Conclusion: The TyG index is an effective clinical tool for predicting CKD risk in patients with primary hypothyroidism and holds important clinical application potential.