Does this test have other names?

Factor V assay, clotting factor tests, factor assay

What is this test?

A factor V test is a blood test that checks for a deficiency in a protein known as factor V. Factor V is a protein that helps your blood to clot. Having too little factor V can cause a rare bleeding disorder. Your body has many protein "clotting factors." They are identified by Roman numerals.

Factor V deficiency is an inherited disorder. It is called an autosomal recessive gene disorder. This means both parents must have the defective gene and pass it on to their children for this to happen.

Why do I need this test?

If you have certain symptoms, such as unexplained or extra 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. You may need 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 blood may be checked for deficiencies in other clotting factors. Prothrombin time and partial thromboplastin times may also be checked.

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 often given as a percentage. So if you get a result of 100%, it means your factor V is at 100% of its normal value. Levels between 20% and 70% mean a mild factor V deficiency. This usually causes no symptoms. Levels of 1% to 10% are severely low and can lead to major bleeding issues.

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 V is quite rare (about 1 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 happen after exposure to some toxins.

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.