Blood coagulation and fibrinolytic activity in hypothyroidism.

The influence of hypothyroidism on haemostasis is controversial; both hypocoagulable and hypercoagulable states have been reported. Hypothyroidism has been associated with atherosclerosis; a hypercoagulable state in addition might represent a risk factor for thromboembolic disease. The aim of the present study was to investigate the markers of endogenous coagulation and vascular endothelial cell function and to evaluate the relationship between serum lipid profile, thyroid hormones and haemostatic parameters in hypothyroid patients. We investigated various haemostatic parameters in 20 patients with hypothyroidism and compared them with 20 euthyroid controls. The relationship between serum thyroid hormones and the haemostatic parameters was examined. The plasma levels of fibrinogen, AT III and PAI-1 were significantly increased in hypothyroid patients compared with the control group, whereas factors VIII and X activity was decreased. We showed that free T3 levels correlated with factor IX activity. Free T4, FT3 and TSH did not correlate with fibrinogen, vWF, AT III, t-PA, or PAI-1. aPTT correlated inversely with t-PA activity and positively with protein C activity. Anti-Tg correlated inversely with FV. There was a positive correlation between triglycerides and protein C. Protein S correlated inversely with high density lipoprotein cholesterol. We found a hypofibrinolytic state in patients with hypothyroidism. Our results suggest that the risk of developing thrombosis and ultimately myocardial infarction via high PAI-1 levels may be increased in patients with hypothyroidism, a result in line with recent epidemiological data. However, thyroid hormones may play a role at different levels of the complex haemostatic system.