Do variations in thyroid hormone indices within the euthyroid range relate to structural severity of diabetic nephropathy (DN)? A cross-sectional study published in Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy evaluated associations between thyroid hormone indices and biopsy-confirmed DN severity in patients with type 2 diabetes mellitus (T2DM).

The analysis included 362 euthyroid adults with T2DM and biopsy-proven DN. Renal lesions were classified according to the Renal Pathology Society criteria into early (class I–II) and advanced (class III–IV) DN. Serum free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), and the FT3/FT4 ratio were measured. Multivariable logistic regression and restricted cubic spline analyses were used to evaluate associations.

Of the cohort, 143 patients had early DN and 219 had advanced DN. Patients with advanced DN had lower FT3 levels (4.46 ± 0.66 vs 4.82 ± 0.73 pmol/L; P < 0.001) and lower FT3/FT4 ratio (median 0.31 vs 0.33; P = 0.013). Lower FT3 levels were independently associated with higher odds of advanced DN (OR 0.442; 95% CI 0.293-0.666; P < 0.001). Higher FT3 quartiles were associated with progressively lower odds of advanced DN (Q4 vs Q1: OR 0.160; P for trend < 0.001).

In sensitivity analyses adjusting for estimated glomerular filtration rate and diabetic retinopathy, the association between FT3/FT4 ratio and advanced DN was attenuated, while the association for FT3 remained consistent.