Activation of the factor VII-tissue factor pathway.

Advances in our knowledge of the biochemistry of coagulation have facilitated the development of sensitive and specific assays that are able to detect the generation of coagulation enzymes in vivo. It has been demonstrated that the factor VII-tissue factor pathway functions under normal conditions to generate factor Xa and convert prothrombin to thrombin. Furthermore, the factor VII-tissue factor pathway is also mainly responsible for the activation of factor IX with minimal contribution from the contact phase. However the relatively high levels of factor IXa generated are unable to convert factor X to factor Xa under basal conditions. Prospective studies are required to determine whether "biochemically" hypercoagulable individuals (i.e., those with elevated levels of free factor VIIa, activation peptides of factor IX, factor X, or prothrombin) are more likely to develop arterial or venous thrombosis.