Blood Test: von Willebrand Factor (vWF) Antigen

What Is a Blood Test?

By taking and testing a small sample of a person’s blood, doctors can check for many kinds of diseases and conditions. Blood tests help doctors check how the body’s organs are working and see if medical treatments are helpful. 

To help your child 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 anxious about it, work together on ways to stay calm.

What Is a vWF Antigen Test?

Proteins called clotting factors are needed for blood to clot properly and help prevent too much bleeding. A von Willebrand factor (vWF) antigen test measures the amount of a clotting factor called von Willebrand factor.

The body's clotting factors work together in a special order, almost like pieces of a puzzle. When the last piece is in place, the clot develops. But if there aren't enough of them, or any of them don't work as they should, it can take longer than normal for blood to clot.

Von Willebrand factor is involved in a few stages of blood clotting. An abnormal gene can make some kids not have enough vWF, or a defective version of it, causing the bleeding disorder von Willebrand disease.

Why Are vWF Antigen Tests Done?

Doctors order the vWF antigen test to help diagnose or monitor the treatment of von Willebrand disease.

Often, doctors do this test along with others to get a fuller picture of clotting ability. These can include:

• clotting time tests such as prothrombin time [PT] and partial thromboplastin time [PTT]
• vWF activity – ristocetin cofactor test
• factor VIII activity test
• factor IX activity test

Factor VIII and vWF circulate in the body bound to one another. So a decreased amount of factor VIII can also mean a decreased amount of vWF.

What if I Have Questions?

If you have questions about the vWF antigen test or what the test results mean, talk to your doctor.