Thyroid Disorders and Hemostasis.

Lower levels of free thyroxine (whether this is endogenous or exogenous) lead to a hypocoagulable state, and higher levels of free thyroxine lead to a hypercoagulable state. In this narrative review, the effects of different levels of thyroid hormones on clinical end points are described. Hypothyroidism is associated with an increased bleeding risk, whereas hyperthyroidism leads to an increased risk of venous thrombosis. Besides, effects of thyroid hormone on the heart may indirectly influence hemostasis. Hyperthyroidism leads to a higher incidence of atrial fibrillation and atrial flutter, and, at least partly by that mechanism, a higher risk of cerebral arterial thrombosis. In addition, compression effects of goiter on developing venous thrombosis are described. This is caused by local stasis of blood due to tumor expansion.