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. A deficiency of factor X in the blood is a rare bleeding disorder. It affects about 1 person in 1 million. When it happens, it can lead to abnormal or excessive bleeding. 

Why do I need this test?

You may need this test if you have unexplained or excessive bleeding. It may mean your blood is not clotting correctly. You might have a deficiency in one of the clotting factors, such as factor X. Your healthcare provider may run a blood test to check for the presence and function of each of the factors to find out if you have a deficiency.

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

What other tests might I have along with this test?

You may also need tests to check for deficiencies in other clotting factors, as well as other clotting tests.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

In a test of your clotting factors, the results are typically presented as a percentage. Normal ranges are 45% to 155% of normal. In most cases, symptoms appear with levels between 10% and 40%. Some people affected with factor X deficiency have levels as low as 1%. This is considered a severe form of the disease. 

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be 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. This is called an acquired factor X deficiency. These include liver disease, cancers, vitamin K deficiency, and exposure to environmental toxins. This can cause a short-term 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. Tell your healthcare provider about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.