Levothyroxine (LT4) suppression treatment for benign thyroid nodules alters coagulation.

Objective: Endogenous hyperthyroidism is associated with altered coagulation. The aim of the present study is to investigate the effect of levothyroxine (LT(4)) suppression treatment for benign thyroid nodules on coagulation system.
Design: Prospective case-control study. Patients Thirty consecutive euthyroid pre-menopausal women with nodular goitre disease and 28 healthy controls were included in the study.
Measurements: Plasma fibrinogen, d-dimer, von Willebrand factor (vWF), tissue factor (TF), tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI-1) and tissue factor pathway inhibitor (TFPI) levels were measured at baseline and after LT(4) suppression therapy.
Results: Plasma levels of fibrinogen, d-dimer, vWF, TF and PAI-1 increased significantly after treatment with LT(4) for 1 year. Serum FT(4) was a significant predictor of increased fibrinogen, vWF and PAI-1 levels, when the data was controlled for age and BMI.
Conclusions: Our results suggest that LT(4) suppression therapy for benign thyroid nodules is associated with enhanced coagulation.