The International Society on Thrombosis and Haemostasis (ISTH) is a global not-for-profit organization advancing the understanding, prevention, diagnosis and treatment of thrombotic and bleeding disorders. The ISTH has body of experts in this field which has regular members’ meetings, sets standards for the laboratory testing of blood clotting, and publishes a medical journal, the Journal of Thrombosis and Haemostasis.
The contact activation pathway begins with formation of the primary complex on collagen by high-molecular-weight kininogen(HMWK), prekallikrein, and FXII (Hageman factor). Prekallikrein is converted to kallikrein and FXII becomes FXIIa. FXIIa converts FXI into FXIa. Factor XIa activates FIX, which with its co-factor FVIIIa form the tenase complex, which activates FX to FXa. The minor role that the contact activation pathway has in initiating clot formation can be illustrated by the fact that patients with severe deficiencies of FXII, HMWK, and prekallikrein do not have a bleeding disorder. Instead, contact activation system seems to be more involved in inflammation.