What Is a von Willebrand Factor (vWF) Antigen Test?

Proteins called clotting factors are needed for blood to clot properly and help prevent too much bleeding. A 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.

vWF is involved in a few stages of blood clotting. A gene mutation (change in a gene) can make some kids not have enough vWF, or a defective version of it, causing the bleeding disorder von Willebrand disease.

Rarely, vWF can be low due to problems with the thyroid, bone marrow, or blood cells or an autoimmune condition.

Why Are vWF Antigen Tests Done?

Doctors order the vWF antigen test to help diagnose or monitor the treatment of von Willebrand disease. Kids may need the test if they have bleeding like:

• lots of nosebleeds or easy bruising
• heavy periods that last a long time
• long-lasting or a lot of bleeding during and after procedures (like having a tooth or tonsils removed)
• cuts that ooze blood for longer than usual

Top Things to Know

• A von Willebrand factor (vWF) antigen test checks how much vWF is in the blood.
• The test is done to help spot a bleeding disorder called von Willebrand disease or keep track of its treatment.
• Kids may need to stop taking certain medicines before the blood test.
• Your doctor can explain what it means if vWF antigen levels are high or low.

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 vWF Antigen Test Results Mean?

Your doctor will explain what the results of the vWF antigen test mean for your child. A “normal” level of vWF antigens can vary based on things like age, sex, and the type of von Willebrand disease.

High vWF Antigen Level

If the level of vWF antigens is high (or elevated), it might be due to things like:

• inflammation (including blood vessel inflammation)
• liver problems or a blood disorder
• stress
• exercise
• estrogen use (like with birth control) or pregnancy

Low vWF Antigen Level

The level of vWF antigens may be low because of von Willebrand disease that’s inherited or linked to certain conditions. These may include autoimmune disorders, other blood disorders, or thyroid or heart problems.

Kids with type O blood might also have a low level of vWF antigens.

What Other Tests May Be Done?

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

• clotting time tests like prothrombin time (PT) and partial thromboplastin time (PTT)
• vWF activity – ristocetin cofactor test
• factor VIII activity test
• factor IX activity test

What Else Should I Know?

Kids with von Willebrand disease might need to have the vWF antigen test and other blood tests several times. This is because the levels the tests check may rise and fall over time due to stress, illness, and hormone levels.

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