Effect of levothyroxine suppression therapy on plasma thrombin activatable fibrinolysis inhibitor antigen levels in benign thyroid nodules.

Objective: The aim of this prospective study was to investigate the effect of LT4 suppression therapy on plasma thrombin activatable fibrinolysis inhibitor (TAFI) antigen and plasminogen activator inhibitor-1 (PAI-1) levels in benign thyroid nodules. We also compared hyperthyroid patients and healthy controls.

Methods: Twenty premenopausal women with benign thyroid nodules were given LT4 suppression therapy for 1 year. Plasma TAFI and PAI-1 antigen levels were measured at baseline and after LT4 suppression treatment. The endogenous hyperthyroid group was composed of 19 premenopausal females with newly diagnosed endogenous hyperthyroidism. Eighteen age-matched euthyroid healthy premenopausal women were enrolled as the control group.

Results: TAFI antigen levels decreased after LT4 suppression treatment; however, the difference was not statistically significant (p = 0.057). LT4 treatment resulted in a nonsignificant increase in PAI-1 levels. Patients with endogenous hyperthyroidism had decreased levels of TAFI antigen and increased levels of PAI-1 antigen (p < 0.05). There was a negative correlation between the FT(4) and TAFI antigen levels. Serum TSH was positively correlated with the plasma levels of TAFI antigen.

Conclusions: LT4 suppression therapy for benign thyroid nodules did not result in a significant decrease in TAFI antigen levels in premenopausal women, but endogenous hyperthyroidism was associated with significantly decreased levels of TAFI antigen.