Thyroid dysfunction and hemostasis: an issue still unresolved.

Thyroid hormones exert various effects on the hemostatic system, as documented by the fact that subclinical or overt thyroid dysfunctions may be associated with hypocoagulable or hypercoagulable states. In this review, the hemostatic balance (primary hemostasis, coagulation factors, and fibrinolytic system) in different thyroid disorders is analyzed from a laboratory, pathogenic, and clinical point of view. Although limited, the published studies suggest that patients with hyperthyroidism or subclinical hypothyroidism have an increased thrombotic risk, whereas patients with overt hypothyroidism have a bleeding tendency. Further trials on larger series of patients are needed to confirm these preliminary findings and to elucidate the pathogenic mechanisms regulating the complex interaction between thyroid disorders and hemostasis.