Hemostasis in Hypothyroidism and Autoimmune Thyroid Disorders

CONTEXT There are contradictory results on the effect of hypothyroidism on the changes in hemostasis. Inadequate population-based studies limited their clinical implications, mainly on the risk of venous thromboembolism (VTE). This paper reviews the studies on laboratory and population-based findings regarding hemostatic changes and risk of VTE in hypothyroidism and autoimmune thyroid disorders. EVIDENCE ACQUISITION A comprehensive literature search was conducted employing MEDLINE database. The following words were used for the search: Hypothyroidism; thyroiditis, autoimmune; blood coagulation factors; blood coagulation tests; hemostasis, blood coagulation disorders; thyroid hormones; myxedema; venous thromboembolism; fibrinolysis, receptors thyroid hormone. The papers that were related to hypothyroidism and autoimmune thyroid disorder and hemostasis are used in this review. RESULTS Overt hypothyroidism is more associated with a hypocoagulable state. Decreased platelet count, aggregation and agglutination, von Willebrand factor antigen and activity, several coagulation factors such as factor VIII, IX, XI, VII, and plasminogen activator-1 are detected in overt hypothyrodism. Increased fibrinogen has been detected in subclinical hypothyroidism and autoimmune thyroid disease rendering a tendency towards a hypercoagulability state. Increased factor VII and its activity, and plasminogen activator inhibitor-1 are among several findings contributing to a prothrombotic state in subclinical hypothyroidism. CONCLUSIONS Overt hypothyroidism is associated with a hypocoagulable state and subclinical hypothyroidism and autoimmune thyroid disorders may induce a prothrombotic state. However, there are contradictory findings for the abovementioned thyroid disorders. Prospective studies on the risk of VTE in various levels of hypofunctioning of the thyroid and autoimmune thyroid disorders are warranted.