Role of tissue factor pathway inhibitor in hormone-induced venous thromboembolism.

Exposure to higher levels of steroid hormones, like that in pregnancy or during combined hormonal contraception, increases the risk of venous thromboembolism. Development of resistance to activated protein C (APC) thought to be the underlying pathomechanism of this prothrombotic state. This coagulation phenomena is largely to be explained by the hormone-induced impairment of the protein S/ tissue factor pathway inhibitor (TFPI) leading to a less efficient inactivation of factor Va and factor VIIIa by APC. APC resistance and decreased protein S/TFPI function were associated with the risk of first as well as recurrent venous thromboembolism. Preexisting disturbances in these pathways are likely to predispose to thrombosis during hormone exposure and can persist over years after the thrombosis event.Further studies are necessary to investigate the predictive value of forgoing APC resistance and decreased protein S/TFPI function or an excessive alteration in these parameters during hormone intake on the development of hormone-induced venous thromboembolism.