Factor IX (Antihemophilic Factor B)

Does this test have other names?

Hemophilia B, Christmas disease, factor IX hemophilia, FIX, factor IX deficiency test

What is this test?

The factor IX test is part of a larger screening test to find out what type of bleeding disorder you have. Factor IX is a protein that helps your blood clot. If you are lacking this protein, you may have a bleeding disorder called hemophilia B. Hemophilia B is found mostly in males.

When people with hemophilia get cut or injured, bleeding is hard to stop because their blood does not have normal clotting substances. This is especially dangerous when someone is severely injured. Hemophilia can also cause pain and bleeding inside muscles or joints.

Females carry the gene that causes this disease. But they may not have bleeding problems, except when they menstruate. A female has a 50% chance of passing on the gene that causes the disorder to their children. (A male child would be affected and a female child would be a carrier.) 

Why do I need this test?

You may need this test to confirm that you have hemophilia, which is an inherited disease. A healthcare provider may order this test if your family has a history of bleeding problems. If you're pregnant and have a strong family history, it's especially important to be tested before your baby is born.

This test can be done on a newborn and again when the baby is 6 months old. Older children are often tested if they have large numbers of raised or unusual bruises.

If you're an adult with a history of unusual bleeding problems, your healthcare provider may order this test to see if you have hemophilia. People with milder forms of hemophilia may not have problems until they are older.

If you are worried about having hemophilia but do not have bleeding problems, your healthcare provider may order a genetic test. A genetic test can find the gene that causes hemophilia in most people.

Although hemophilia has no cure, it can be treated once a healthcare provider knows what form of the disease is present.  

What other tests might I have along with this test?

The healthcare provider may also order these other tests to learn more about your bleeding problems:

• Activated partial thromboplastin time (APTT) test. This test identifies clotting problems for factor IX, as well as other clotting substances.

• Prothrombin time (PT) test. This test also identifies clotting problems for factor IX, as well as other clotting substances.

• Complete blood count (CBC). This test measures the number, size, and quality of blood cells.

• Fibrinogen test. This test finds out the level of fibrinogen, a protein that helps blood to clot.

• Clotting factor tests. These tests find out whether you have a bleeding disorder and how severe it is. A person without a bleeding disorder has healthy clotting in 50% to 100% of their blood cells. If you have less than 50%, you may have hemophilia.

• Stool test and urinalysis. These tests may be done to look for blood in your feces and urine. 

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.

This test will tell you if you have the rare form of a bleeding disorder known as hemophilia B. Talk with your healthcare provider about whether you should be tested for other kinds of hemophilia. 

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?

This screening will be positive only if you have the disorder. Infants may need to be retested when they are older if they do not have enough of the factor IX clotting substance at birth.

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 illegal drugs you may use.