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Factor XII assay

  • Definition
    • The factor XII assay is a blood test to measure the activity of factor XII. This is one of the proteins in the body that helps the blood clot.

  • Alternative Names
    • Hageman factor assay

  • How the Test is Performed
  • How to Prepare for the Test
    • Adults do not have to take any special steps to prepare for this test.

  • How the Test will Feel
    • 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.

  • Why the Test is Performed
  • Normal Results
    • A 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 doctor about the meaning of your specific test results.

  • What Abnormal Results Mean
    • Decreased factor XII activity may indicate:

  • Risks
    • Veins and arteries vary in size so it may be harder to take a blood sample from one person than another.

      Other slight risks from having blood drawn may include:

      • Excessive bleeding
      • Fainting or feeling light headed
      • Hematoma (blood accumulating under the skin)
      • Infection (a slight risk any time the skin is broken)
  • References
    • Gailani D, Neff AT. Rare coagulation factor deficiencies. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, Anastasi J, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 139.

      Schmaier AH. Laboratory evaluation of hemostatic and thrombotic disorders. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, Anastasi J, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 131.