Summary
The shortening of the one-stage prothrombin time of plasma brought about by increased foreign surface contact is dependent upon “activation” of factor VII. This activation of VII is the result of a series of activations involving factors XII, IX and probably XI as well. In this it is similar to the activation of factor VIII. Although the prothrombin time in an individual with hemophilia B or the Hageman trait is ‘‘normal”, no shortening occurs after increased foreign surface contact. Factor VII deficient plasma with normal levels of factors XII and IX is “activated” by “contact” in proportion to the level of VII present. No increase in activity of factors II, V, or X was observed after increased foreign surface contact.
