Factor IX Activity Blood Test

What Is a Factor IX Activity Blood Test and Why Is It Done?

A factor IX (factor 9) activity blood test shows how well a protein in the blood called factor IX is working to help a person's blood to clot. Clotting helps prevent too much bleeding.

The test can help:

• Diagnose a blood disorder called hemophilia B. Doctors may order a factor IX activity blood test if a child bleeds longer than normal after an injury or surgery, or has other unusual bleeding.
• Monitor the treatment of hemophilia B.
• Find the reason for an abnormal (unusual) result on other blood clotting tests, like partial thromboplastin time (PTT).

What Is Factor IX?

Factor IX is a kind of protein called a clotting factor. Clotting factors help blood clot properly and help prevent too much bleeding.

The body's blood clotting factors are numbered using the Roman numerals I through XIII. They work together in a special order, almost like pieces of a puzzle. When the last piece is in place, the clot develops — but if even one piece is missing or defective (not working properly), the puzzle can't come together.

Factor IX, along with factor VIII, is involved in the creation of a "net" that closes a torn blood vessel. An abnormal gene can make some kids not have enough factor VIII, causing the bleeding disorder known as hemophilia A. Factor IX deficiency (not having enough factor IX) is known as hemophilia B.

Top Things to Know

• The factor IX activity blood test measures the level of a protein in the blood called factor IX (factor 9).
• Doctors use it to help diagnose hemophilia B and explain unusual results on other clotting tests.
• Kids might need to stop taking certain medicines or not eat or drink before the blood test.
• Your doctor can explain what it means if factor IX activity is low or high.

How Can I Help My Child Prepare for a Blood Test?

To help kids get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test.

If your child is nervous about it, work together on ways to stay calm. Deep breathing or even imagining being in a place that makes your child feel safe and relaxed can help.

What Do Factor IX Activity Test Results Mean?

Your doctor will explain what the results of the factor IX activity test mean for your child. What’s “normal” varies based on things like age and gender.

Low Factor IX Activity

With a low level of factor IX activity, the factor IX protein isn’t working well, so blood isn’t clotting as it should. This could be due to:

• hemophilia B or another blood disorder
• the body not getting enough fat from food
• too little vitamin K
• a liver problem
• a blood thinner (medicine that thins the blood)

High Factor IX Activity

With a high level of factor IX activity, the factor IX protein is working too hard, so blood is clotting too much. This may cause blood clots in places like veins, which could be serious.

What Else Should I Know?

If you have questions about the factor IX activity test, other hemophilia tests, or what the results mean, talk to your doctor.