AIM: Subclinical hypothyroidism (SCH) is frequently observed in patients with type 2 diabetes mellitus (T2DM) and may exacerbate macrovascular complications due to its impact on metabolic and thyroid function parameters. This study aims to explore the association between varying levels of thyroid-stimulating hormone (TSH) and the risk of macrovascular complications, alongside analyzing key metabolic, demographic, and clinical factors in T2DM patients with SCH. METHODS: A retrospective study was conducted at the Second Affiliated Hospital of Dalian Medical University, and data was collected from 2017 to 2023. According to their TSH levels, 305 patients were divided into three groups, which were T2DM mild SCH (TSH 4.34-6.9 mIU/L), T2DM moderate SCH (TSH 7.0-9.9 mIU/L), and T2DM severe SCH (TSH levels of 10.0 mIU/L or higher). The chi-square test was used for categorical variables, while one-way analysis of variance (ANOVA) was used for continuous variables. Univariate and multivariate binary logistic regression analysis was performed to determine the risk of macrovascular complications. Further, a statistical significance was set at p <
0.05. RESULTS: Patients with severe SCH had the highest incidence of macrovascular complications, 19 (90.5%), followed by moderate SCH 38 (80.9%) and mild SCH 142 (59.9%) (p <
0.001). Multivariate analysis revealed a 4.35-fold increased risk (OR: 4.352, 95% CI: 1.761-10.754, p = 0.001) for macrovascular complications in moderate SCH and a 6.08-fold increased risk (OR: 6.075, 95% CI: 1.202-30.715, p = 0.029) in severe SCH compared to mild SCH. Age group 65 and older, male sex, and severe SCH were significant predictors of macrovascular complications. Peripheral artery disease (PAD) and coronary artery disease (CAD) were particularly associated with severe SCH (OR: 5.913, p <
0.001
OR: 3.268, p = 0.013, respectively). CONCLUSION: T2DM patients with severe or moderate SCH are at significantly higher risk of macrovascular complications, especially PAD and CAD. Timely intervention and close monitoring of TSH levels, particularly in older and male patients, are essential to mitigate these risks.