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. It can help find out whether you have a bleeding or blood clotting disorder. The test can also screen for liver problems. Factor II, also called prothrombin, is made in your liver.
Prothrombin must be present in your blood for a clot to form. Prothrombin and other similar proteins are called coagulation factors. Prothrombin is also called factor II because it is one of many proteins, or factors, that must appear in your blood for clotting to happen.
Why do I need this test?
You may need this test if you have bled often or for a long time. 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:
You may also need this test if you develop abnormal blood clots in your blood vessels. You may develop abnormal blood clots 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 doctor may also order this test if:
You have other abnormal blood tests that suggest a clotting problem
Your health care 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?
Your health care provider may also order 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, or PT, blood test. This measures the activity of prothrombin along with other proteins that help blood clot.
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses to do the test. Even 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.
Health care providers chart the results of your test in percentages. They then compare your sample with a laboratory control called a reference value. Normal results for people 18 and older are within 80 to 120 percent of this baseline. Abnormal results may mean you have:
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. 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 drug Coumadin (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. 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.
- Haines, Cynthia, MD
- Petersen, Sheralee, MPAS, PA-C