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. 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 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:
Blood in your stools
Long-lasting bleeding after surgery
Heavy menstrual periods
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 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?
Your healthcare 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, and international normalized ratio (INR) 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, the method used for the test, and other things. Your test results 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 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. 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. Be sure your healthcare provider 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.
October 03, 2017
Clinical use of coagulation tests. UpToDate, McPherson. Henry's Clinical Diagnosis and Management by Laboratory Methods. 2017, 23rd ed., pp. 794-811.
Fraser, Marianne, MSN, RN,Haldeman-Englert, Chad, MD