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Factor V

Does this test have other names?

Factor V assay, clotting factor tests

What is this test?

A factor V test is a blood test that checks for a deficiency in a protein known as factor V. This protein helps the blood to clot. Your body has a number of protein "clotting factors." They are identified by Roman numerals – factor I and factor II, for instance. A deficiency of factor V is quite rare, but when it occurs, it can lead to bleeding problems.

Why do I need this test?

If you have certain symptoms, such as unexplained or excessive bleeding or bruising, it may mean that your blood is not clotting the way it should. You might have a deficiency in one of the clotting factors. Your health care provider may do a blood test to check for the presence and function of the individual clotting factors to see if you have a deficiency in any of them.

What other tests might I have along with this test?

Along with tests to check for factor V deficiency, your health care provider might check your blood 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 usually given as a percentage. So, if you get a result of 100 percent, it means your factor V is at 100 percent of its normal value. Levels between 25 and 60 percent indicate a mild factor V deficiency. This usually causes no symptoms. Levels of 1 to 10 percent are severely low and can lead to major bleeding issues.

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?

A deficiency of factor V is quite rare (about one in 1 million) and can be a genetic disorder passed on from parents to their children. But some clotting factors, including factor V, can decrease because of certain illnesses, such as liver disease, cancers, autoimmune diseases, and a disease called disseminated intravascular coagulation. It can also occur after exposure to some toxins.

How do I get ready for this test?

You don't need to prepare for this test.