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.
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
No special preparation is needed.
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
Your health care provider may want you to have this test if you had abnormal results on the partial thromboplastin time (PTT) blood-clotting test. You may also need the test if a family member is known to have factor XII deficiency.
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 provider about the meaning of your specific test results.
What Abnormal Results Mean
Decreased factor XII activity may indicate:
- Factor XII deficiency (a bleeding disorder caused by a lack of blood clotting factor XII)
- Liver disease
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Multiple punctures to locate veins
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Hageman factor assay
Chernecky CC, Berger BJ. Factor XII (Hageman factor) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:508-509.
Gailani D, Neff AT. Rare coagulation factor deficiencies. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 137.
Review Date 1/29/2019
Updated by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.