Evaluation of the respective influence of thyroid hormones and TSH on blood coagulation parameters after total thyroidectomy.

Background: Several hemostatic abnormalities have been described in hypothyroidism, such as modification of coagulation proteins and bleeding tendency. Although thyroid hormone deficiency is considered to be responsible for these changes, the underlying mechanisms have not yet been established.

Objective: To evaluate the respective influence of peripheral thyroid hormones (free thyroxine) and TSH on blood clotting by assessing coagulation parameters in patients with a history of total thyroidectomy for thyroid cancer, under three different conditions: induced hypothyroidism, euthyroid state, and following recombinant human TSH (rhTSH) administration.

Methods: Coagulation parameters (platelet count, fibrinogen, international normalized ratio, prothrombin time, thrombin time, activated partial thromboplastin time (APTT), factor VIII activity ((FVIII:C), as well as von Willebrand factor antigen (VWF:Ag) and VWF activity using collagen binding assay (VWF:CBA)) were measured in patients with severe hypothyroidism following withdrawal of thyroid hormone replacement therapy, and in the same patients with euthyroidism after restoring replacement treatment (group A), and before and after administering rhTSH (group B).

Results: FVIII:C, VWF:Ag, and VWF:CBA were significantly decreased (P<0.001), whereas APTT was significantly increased (P<0.001) in patients with severe hypothyroidism compared with patients in the euthyroid state. No changes in clotting parameters were observed in patients who received rhTSH therapy.

Conclusion: This prospective study shows that severe short-term hypothyroidism is associated with significantly lower levels of VWF:Ag, VWF:CBA, and FVIII:C. Administration of exogenous TSH has no effect on coagulation parameters. These findings suggest that thyroid hormone deficiency is likely to be the main cause of coagulation alterations in patients with hypothyroidism.