Factor XII Activity Test

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.

Blood test is required to measure the activity of factor XII. When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away. Decreased factor XII activity may indicate: Inherited (congenital) deficiency of factor XII. Factor XII deficiency is rarely found to be associated with bleeding, but several case studies have reported thromboembolic events in FXII-deficient patients. Factor XII testing is indicated when factor XII deficiency is suspected. No hemorrhagic diathesis is associated with congenital factor XII deficiency.

Diagnosing deficiency of coagulation factor XII. Determining cause of prolonged activated partial thromboplastin time.

The risk for perioperative bleeding with isolated factor XII deficiency is considered to be that of the average patient. Your health care provider may want you to have this test if you had abnormal results on the partial thromboplastin time blood-clotting test.

You may also need the test if a family member is known to have factor XII deficiency. The normal value is 50% to 200% of the laboratory control or reference value. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.