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Factor XII

Does this test have other names?

Coagulation factor XII, F12, FA12-human, HAE3, HAEX, HAF, Hageman factor

What is this test?

This test measures the amount of a protein called coagulation factor XII in your blood.

Factor XII is part of a group of proteins that act in a specific order to create a blood clot after an injury. Factor XII is often called Hageman factor.

Factor XII floats freely in your bloodstream until it's needed. When factor XII comes in contact with the damaged wall of a vein, it activates coagulation factor XI. That interaction sets off a chain reaction, called a coagulation cascade, to form a blood clot. Clotting closes off the open vein and prevents excessive blood loss. Factor XII also stimulates inflammation and swelling, which are normal body responses to injury and infection.

The F12 gene is responsible for your body making coagulation factor XII. Mutations in this gene are involved with hereditary angioedema type III and factor XII deficiency.

Hereditary angioedema type III is an extremely rare disorder. Symptoms include severe swelling of the arms and legs, face, intestines, and airways.

Factor XII deficiency is a hereditary disorder. It's usually discovered during routine blood testing. If you have a low level of coagulation factor XII and no other problems with the clotting process, you won't have problems with abnormal bleeding or forming blood clots when you are cut or injured. The deficiency is actually found in a blood test because a low level of factor XII causes your blood to take longer to coagulate in the test tube, even if this doesn't occur in your body.

Low levels of Factor XII have been linked with thrombosis. Thrombosis means that a clot forms within a blood vessel and causes a partial or complete blockage. But doctors aren't sure exactly how thrombosis is related to factor XII deficiency.

This test is usually part of an activated partial thromboplastin time (aPTT) test, which measures the clotting activity of several factors, including factor XII.

Why do I need this test?

You may have test if you've had recent bleeding or your doctor wants to check your risk of bleeding before you have surgery.

What other tests might I have along with this test?

Your doctor may also order a prothrombin time test to look at specific factors in your coagulation cascade.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in seconds of time, showing how long it takes your blood sample to clot.

Normal values are:

  • 25 to 41 seconds

  • 1.5 to 2.5 minutes if you take certain anticoagulation medications

Each factor must be present and working properly in order to form a clot. A longer clotting time may mean that you have an inherited deficiency of factor XII.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Taking heparin or any other thrombin inhibitor will affect your results.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.