Thyroid Hormones and Autoantibodies as Markers for Diabetic Nephropathy in Patients with Type 2 Diabetes Mellitus

Background: Among the complications of type 2 diabetes mellitus (T2DM), diabetic nephropathy (DN) is recognized as particularly serious and burdensome. This research aimed to evaluate the predictive role of thyroid function and thyroid autoantibodies in the development of DN among patients with T2DM. Methods: We did this case–control study on 69 subjects divided into three groups: healthy controls (n=23), T2DM without nephropathy (n=23), and T2DM with nephropathy (n=23). Clinical, biochemical, renal, and thyroid profiles were assessed, including free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), free thyroxine (FT4), thyroglobulin antibody (TgAb), as well as the thyroid peroxidase antibody (TPOAb). Results: DN patients had significantly higher TSH (2.89 ± 0.94 mIU/L, p=0.002), lower FT3 (4.09 ± 1.63 pmol/L, p=0.004), and elevated thyroid autoantibodies (TgAb 1.34 ± 0.15; TPOAb 0.57 ± 0.14, both p<0.001). FT3 had negative correlations with HbA1c (r=-0.27), ACR (r=-0.44), and creatinine (r=-0.25), while TSH had positive correlations with ACR (r=0.49) and inversely with eGFR (r=-0.35). ROC analysis showed high diagnostic performance for TPOAb (AUC=0.884; Sens 88.3%; Spec 95.7%) and TgAb (AUC=0.860), followed by TSH (AUC=0.816) and FT3 (AUC=0.790). Multivariate regression confirmed elevated TSH (OR 4.59, 95% CI 1.79–11.72), reduced FT3 (OR 0.03, 95% CI 0.004–0.29), TgAb (OR 1.24, 95% CI 1.03–1.52), TPOAb (OR 1.93, 95% CI 1.01–3.70), and triglycerides (OR 2.09, 95% CI 1.31–3.33) as independent predictors of DN. Conclusion: Elevated TSH, reduced FT3, and thyroid autoantibodies particularly TPOAb demonstrated strong predictive accuracy for DN in T2DM and could serve as valuable biomarkers for early risk stratification.