Hidden impact: How subclinical hypothyroidism influences renal outcomes in type 2 diabetes mellitus

Objectives: Type 2 diabetes mellitus (T2DM) frequently presents with multiple complications, including subclinical hypothyroidism (SCH) and diabetic kidney disease. The purpose of this research was to examine whether subclinical thyroid dysfunction influences the onset and advancement of diabetic nephropathy (DN) among individuals with type 2 diabetes. Materials and Methods: A cross-sectional study was conducted with 368 patients with T2DM. Thyroid function tests, urinary albumin-to-creatinine ratio (UACR), estimated glomerular filtration rate (eGFR), and other relevant clinical parameters were assessed. Patients were categorized based on thyroid status (euthyroid or SCH) and nephropathy status. The association between SCH and DN was analyzed using multivariate logistic regression models. Results: Among 368 T2DM patients, 61 (16.6%) had SCH, whereas 275 (74.7%) were euthyroid. DN was significantly more prevalent in patients with SCH compared to euthyroid patients (54.1% vs. 25.8%, P < 0.001). Following statistical correction for potential confounders such as patient age, gender, diabetes duration, blood pressure status, body mass index, and glycemic control, subclinical thyroid dysfunction continued to demonstrate an independent relationship with diabetic kidney disease (adjusted odds ratio: 4.30, 95% confidence interval: 2.25–8.20, P < 0.001). Patients with SCH showed significantly higher UACR levels (62.45 ± 48.25 vs. 28.15 ± 24.80 mg/g, P < 0.001) and lower eGFR (78.35 ± 16.42 vs. 89.78 ± 14.25 mL/min/1.73 m 2 , P < 0.001) compared to euthyroid patients. Significant correlations were observed between thyroid-stimulating hormone (TSH) levels and renal function parameters (r = 0.487 for UACR, r = −0.398 for eGFR, both P < 0.001), with a clear dose–response relationship across TSH quartiles. Conclusion: SCH is significantly associated with an increased prevalence of DN in patients with T2DM. The strength of association increases after adjusting for traditional risk factors, with particularly strong effects in hypertensive patients and those with longer diabetes duration. These findings suggest that thyroid function assessment may be warranted in T2DM patients with renal impairment; however, prospective studies are needed to determine whether SCH management can improve renal outcomes.