Metabolic and hepatic differences among biochemically euthyroid individuals with distinct thyroid hormone sources: a...

This study aimed to evaluate the associations between thyroid hormone profiles and derived ratios (particularly the T3/T4 ratio), body composition parameters, and markers of hepatic steatosis and fibrosis in biochemically euthyroid individuals with distinct thyroid physiologies. Specifically, we sought to compare patients without endogenous thyroid hormone production following total thyroidectomy, patients with Hashimoto's thyroiditis, and healthy controls.

In this retrospective, cross-sectional study, three groups with serum TSH levels within the reference range were included: (i) patients with hypothyroidism due to Hashimoto's thyroiditis (HT, n = 123), (ii) patients who had undergone total thyroidectomy (TT, n = 103) for benign conditions, and (iii) healthy control subjects (C, n = 83). Thyroid hormone levels and ratios (T3/T4, T3/TSH, T4/TSH), anthropometric measurements, body composition parameters, and non-invasive indices of hepatic steatosis and fibrosis (Fatty Liver Index (FLI) and Fibrosis-4 index (FIB-4)) were assessed in all participants.

The T3/T4 ratio differed significantly across groups (controls > HT > TT; p < 0.001). Both patient groups exhibited higher FLI (p = 0.019) and FIB-4 (p = 0.002) scores than controls. In correlation analyses, the T3/T4 ratio was positively associated with FIB-4 exclusively in the TT group (r = 0.263, p = 0.007). In hierarchical multiple regression restricted to TT patients, age independently predicted FIB-4 (β = 0.553, p < 0.001), whereas visceral fat rating was not significant (p = 0.476). After adjustment for age and visceral adiposity, the T3/T4 ratio remained an independent predictor of FIB-4 (β = 0.201, p = 0.016). Although TT patients showed less favorable body composition (higher fat mass and visceral adiposity; lower muscle and bone mineral percentages), these parameters did not independently predict FIB-4.

These findings demonstrate that thyroid hormone balance is not homogeneous even under biochemically euthyroid conditions and that differences in functional thyroid capacity may translate into distinct metabolic and hepatic consequences. Thyroid hormone ratios may therefore provide complementary clinical information, supporting a more tissue-oriented approach to the evaluation of the thyroid-liver axis.

Not applicable.