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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

A blood sample is needed.

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

Your doctor 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.

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.


Review Date: 1/27/2015
Reviewed By: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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