Thyroid disorders and hypercoagulability

Various abnormalities of coagulation and fibrinolysis, ranging from subclinical laboratory abnormalities to clinically significant disorders of hemostasis, but rarely major hemorrhage or thromboembolism, may occur in patients with thyroid diseases. This review discusses the relationships between thyroid dysfunction and the coagulation/fibrinolytic system. According to the recent literature, most of the coagulation/fibrinolytic abnormalities associated with thyroid dysfunction are the consequences of direct effects of thyroid hormones on the synthesis of various hemostatic parameters. Thyroid autoimmunity may also modify the processes of secondary hemostasis. Hyperthyroidism is generally associated with hypercoagulability and hypofibrinolysis, whereas the hemostatic profile in hypothyroidism depends on the severity of the disease. Both hypercoagulable and hypocoagulable states including increased fibrinolytic activity have been reported in hypothyroidism. Few data are available on hemostasis in subclinical thyroid diseases. In conclusion, adequate further prospective clinical studies of high quality including a larges series of patients are needed to explain the degree and type of coagulation/fibrinolytic abnormalities in patients with thyroid diseases.