Does this test have other names?
FXI, factor XI deficiency test, test for hemophilia C
What is this test?
This test measures the amount of factor XI in your blood. Factor XI is a protein that
plays an important role in blood clotting.
If you don't have enough factor XI, you may have a condition called factor XI deficiency.
This is a rare bleeding disorder. It is also known as hemophilia C. Hemophilia C is
a bleeding disorder that can range from mild to moderate. If you have hemophilia C,
your tendency to bleed is not as severe as that seen in the other types of hemophilia.
Why do I need this test?
You might need this test if your healthcare provider suspects that you have factor
What other tests might I have along with this test?
Your healthcare provider may order different types of blood-clotting tests. These
Activated partial thromboplastin time, or aPTT, test, which shows the activity of several substances involved in blood clotting
Prothrombin time, or PT, test, which measures how long it takes your blood to form a clot
Platelet count, which is normally done if a bleeding disorder is suspected
Thrombin time, which measures how quickly your body makes fibrin, a protein that is part of the
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 units per deciliter (U/dL). The normal range for factor XI activity
levels is 70 to 150 U/dL, or 70% to 150%.
If your results are lower than normal, it means you may have factor XI deficiency.
This condition is quite rare and occurs most often among Ashkenazi Jews.
If your results are less than 15% of normal, you may have severe factor XI deficiency.
People with factor XI deficiency also usually have a prolonged aPTT along with normal
thrombin and prothrombin times.
If your results are 20% to 70% of normal, you may have a mild deficiency. The only
way to make a sure diagnosis is to do more testing.
Levels outside the normal range may also mean that you have liver disease or a vitamin
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?
Other factors aren't likely to 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.