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
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
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 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 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
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 healthcare
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
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
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 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. But 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.