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.
A deficiency in factor XII is a rare bleeding disorder, but it causes abnormal clotting
rather than bleeding.
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. This forms a blood
clot. Clotting closes off the open vein and keeps you from losing too much blood.
Factor XII also stimulates inflammation and swelling. These 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 an inherited 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 healthcare
providers 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 healthcare provider wants
to check your risk of bleeding before you have surgery.
What other tests might I have along with this test?
Your healthcare provider 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 healthcare
Results are given in seconds of time, showing how long it takes your blood sample
Normal values for the aPTT test are:
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
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 healthcare provider 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.