Factor XII, factor XI, high–molecular-weight kininogen, and prekallikrein are referred to as the contact factors. Individuals who are deficient in any of these factors do not have a hemorrhagic diathesis, even after significant trauma or surgery. However, factor XII, HK, PK and complement factor C1q participate in inflammatory responses that involve blood coagulation, fibrinolysis, and generation of kinins. Factor XII is synthesized in the liver. Its deficiency is associated with an increased tendency toward thrombosis in animal models and perhaps in humans. The gene for factor XII is located on chromosome. Factor XII is responsible for the contact activation of blood coagulation as seen in the activated partial thromboplastin time test.