Various haemostatic abnormalities have been associated with thyroid dysfunction, especially with hypothyroidism. The underlying mechanisms are not well established.
The aim of the study was to evaluate the primary and secondary haemostasis in patients with severe hypothyroidism, to assess the role of thyroid hormone deficiency and to determine whether increased serum TSH level despite normal free thyroid hormone concentrations could influence the coagulation system.
Platelet count, fibrinogen, prothrombin time, activated partial thromboplastin time (APTT), INR, thrombin time, factor VIII activity, factor von Willebrand were measured in 52 patients (age 45±14 years, 40 women and 12 men) with previous total thyroidectomy for differentiated thyroid cancer. Factor von Willebrand and factor VIII activity were significantly decreased while APTT was significantly increased in hypothyroidism (after withdrawing of thyroid hormones) compared to euthyroidism in 22 patients: TSH (μU/ml): 94.3±36.0 vs 1.01±1.44, P<0.001; FT4 (ng/dl): 0.19±0.07 vs 1.3±0.2, P<0.001; factor VIII activity (%): 109.3±39.4 vs 144.5±33.3, P<0.001; factor von Willebrand activity(%): 102.6±40.8 vs 140.5±45.6, P<0.001; factor von Willebrand antigen (%): 97.4±35.9 vs 120.7±33.5, P<0.001; APTT (seconds): 27.8±2.3 vs 25.2±1.6, P<0.001). No changes in all clotting parameters were observed in 30 patients evaluated before administration of recombinant human thyrotropin and at day 3 of the peak of TSH.
This prospective study shows that a short term severe hypothyroidism is associated with significant changes of factor VIII activity and factor von Willebrand. Increased TSH has no effect on coagulation parameters. This suggests that low thyroid hormone concentration is the main possible cause of alteration of coagulation parameters.
Surgery may be thus performed in subclinical hypothyroidism without risk of bleeding