Predictive Effects of FT3/FT4 Ratio in Non-Dialysis Patients with Diabetic Kidney Disease

Background: Diabetic kidney disease (DKD) is a major complication of type 2 diabetes mellitus (T2DM), contributing to morbidity and mortality. Thyroid hormones (THs), particularly the free triiodothyronine (FT3), free thyroxine (FT4), and the free triiodothyronine/free thyroxine (FT3/FT4) ratio, have been implicated in renal outcomes, but their predictive role in DKD remains unclear. Aim: To evaluate the FT3/FT4 ratio as a predictive risk factor for progression of DKD in non-dialysis patients. Methods: This cross-sectional study included 120 participants: 20 healthy controls, 20 T2DM patients without DKD, and 80 T2DM patients with DKD (stages 1–4). All participants underwent clinical assessment and laboratory evaluation, including HbA1c, fasting and postprandial glucose, urinary albumin-to-creatinine ratio (UACR), lipid profile, serum creatinine (SCr), estimated glomerular filtration rate (eGFR), and thyroid function tests (FT3, TSH, FT4). Results: Patients with DKD had significantly reduced FT3/FT4 ratios compared with controls (p-value equal 0.004). Thyroid dysfunction was more frequent in DKD patients, with low T3 syndrome being the most common abnormality (18.8%). Across CKD stages, the FT3/FT4 ratio declined progressively (p < 0.001). Multivariate regression confirmed the FT3/FT4 ratio as an independent predictor of diabetic kidney disease (p=0.009). ROC analysis illustrated that the FT3/FT4 ratio achieved greater sensitivity (81%) than FT3 (64%) or FT4 (65%) for detecting DKD, though specificity remained modest. Conclusion: A reduced FT3/FT4 ratio is independently related to a higher risk of DKD in T2DM cases and may serve as a useful predictor for early recognition and risk stratification.