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Factor II

Does this test have other names?

Factor II assay

What is this test?

This test measures how much of a protein called factor II is in your blood. Factor II is also called prothrombin. This test can help find out whether you have a bleeding or blood clotting disorder. The test can also screen for liver problems. Factor II is made in your liver.

Prothrombin and other similar proteins are called coagulation factors. It is 1 of many proteins, or factors, that you need in your blood for clotting to happen. Factor II deficiency is a disorder that is inherited. It is called an autosomal recessive genetic disorder. This means both parents must carry an abnormal copy of the gene for the disorder and pass it on for a child to have it. 

Why do I need this test?

You may need this test if you bleed often. Or if it takes a long time for bleeding to stop. Prothrombin levels may be low if you have a bleeding disorder. This bleeding disorder can be inherited, or it may have nothing to do with your genes.

Symptoms of a bleeding problem may include:

  • Nosebleeds

  • Blood in your stools

  • Bleeding gums

  • Long-lasting bleeding after surgery

  • Easy bruising

  • Heavy menstrual periods

You may also need this test if you develop abnormal blood clots in your blood vessels. This could happen if you have a genetic problem that causes your liver to make extra prothrombin. Higher levels of prothrombin make it more likely that you will form blood clots, such as a deep vein thrombosis or pulmonary embolism.

Your healthcare provider may also order this test if:

  • You have other abnormal blood tests that suggest a clotting problem

  • Your healthcare providers are screening you for liver disease

  • You have a family history of a bleeding or clotting disorder 

What other tests might I have along with this test?

You may also have other tests to look at the blood clotting process in your body. These types of tests are called coagulation studies. You may also have a prothrombin time and international normalized ratio blood test. This measures the activity of prothrombin along with other proteins that help blood clot. 

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.

Healthcare providers chart the results of your test in percentages. They then compare your sample with a lab control called a reference value. Normal results for people 18 and older are within 80% to 120% of this baseline. Abnormal results may mean you have:

  • Liver or kidney disease

  • A bleeding disorder you were born with

  • Vitamin K deficiency 

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 has 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. If you have a bleeding disorder, you may be slightly more likely to bleed after a blood sample. 

What might affect my test results?

If you are taking the blood-thinner medicine warfarin, it could interfere with your test results. In newborns, prothrombin is normally low.

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.  

Online Medical Reviewer: Chad Haldeman-Englert MD
Online Medical Reviewer: Raymond Turley Jr PA-C
Online Medical Reviewer: Tara Novick BSN MSN
Date Last Reviewed: 9/1/2022
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