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Factor X

Does this test have other names?

Factor assays, clotting factor tests

What is this test?

A factor X test is a blood test that checks for a deficiency in a protein in the blood called factor X. This protein helps with clotting. Your body has a number of protein clotting factors. They are identified by Roman numerals (factor I and factor II, for example). A deficiency of factor X in the blood is very rare, affecting about one person in 1 million. When it occurs, it can lead to abnormal or excessive bleeding. 

Why do I need this test?

If you have unexplained or excessive bleeding, it may mean your blood is not clotting properly. You might have a deficiency in one of the clotting factors, such as factor X. Your doctor may run a blood test to check for the presence and function of the individual factors to find out whether you have a deficiency.

In rare cases, you inherit a factor X deficiency from your parents. You can also acquire a factor X deficiency if you have liver disease or a vitamin K deficiency or if you are being treated with the drug warfarin. 

What other tests might I have along with this test?

Your doctor might also order tests to check for deficiencies in other clotting factors.

What do my test results mean?

A result for a lab test may be affected by many things, including the method the laboratory uses to do the test. 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.

In a test of your clotting factors, the results are typically presented as a percentage. If you get a result of 100 percent, that means your factor X is at 100 percent of its normal value. You will be told that you have a normal test result. Numbers lower than 100 percent indicate low levels of factor X. Some people affected with factor X deficiency have levels as low as 1 percent. 

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, and a sense of lightheadedness. 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?

A deficiency of factor X is rare and can be a genetic disorder. But the levels of some clotting factors, including factor X, can fall because of certain illnesses and conditions. These include liver disease, cancers, vitamin K deficiency, and exposure to environmental toxins. This can cause a temporary change in clotting factor levels that may return to normal at a later time.

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.