Objective  To investigate the correlations of 25-(OH)D₃ and the triglyceride–glucose (TyG) index with type 2 diabetic nephropathy.

Methods A total of 340 patients with type 2 diabetes mellitus (T2DM) were enrolled and divided into the simple diabetes group, the early diabetic nephropathy group, and the diabetic nephropathy group according to the urinary albumin-to-creatinine ratio (UACR). Baseline characteristics were compared among the three groups. Multivariate logistic regression analysis was performed to identify independent risk factors for type 2 diabetic nephropathy. Receiver operating characteristic (ROC) curves were used to evaluate the predictive value of 25-(OH)D₃, the TyG index, and their combination for type 2 diabetic nephropathy.

Results Univariate analysis revealed statistically significant differences among the three groups in FPG, HbA1c, UCr, BUN, UA, Scr, eGFR, NEU, CysC, ALB, TG, HDL, VLDL, ApoB, history of hypertension, 25-(OH)D₃, and the TyG index (P ＜ 0.05 to P ＜ 0.01). Logistic regression analysis demonstrated that low 25-(OH)D₃, high TyG index, low UCr, and comorbid hypertension were risk factors for type 2 diabetic nephropathy (P ＜ 0.05 to P ＜ 0.01). ROC curve analysis demonstrated that the area under the curve (AUC) for 25-(OH)D₃ and the TyG index were 0.789 (95% CI: 0.742 ~ 0.836, P ＜ 0.01) and 0.731 (95% CI: 0.678 ~ 0.783, P ＜ 0.01), respectively. The combined AUC of both indices was 0.855 (95% CI: 0.816 ~ 0.893, P ＜ 0.01).

Conclusions 25-(OH)D₃ and the TyG index are associated with type 2 diabetic nephropathy, and their combined detection has important clinical value in improving the predictive efficacy for diabetic nephropathy.