[Skip to Content]
Find care at Nemours Children's HealthDoctorsLocations

Blood Test: von Willebrand Factor (vWF) Activity - Ristocetin Cofactor

Reviewed by: Larissa Hirsch, MD
  • Listen
      mp3

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 Activity – Ristocetin Cofactor Test?

Proteins called clotting factors help blood clot properly and help prevent too much bleeding. A von Willebrand factor (vWF) activity – ristocetin (riss-teh-SEE-tin) cofactor test lets doctors see how a protein called von Willebrand factor is working.

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 Activity – Ristocetin Cofactor Tests Done?

Doctors order the vWF activity – ristocetin cofactor test (also called von Willebrand activity test or RCF activity 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:

What if I Have Questions?

If you have questions about the vWF activity – ristocetin cofactor test or what the test results mean, talk to your doctor.

Reviewed by: Larissa Hirsch, MD
Date reviewed: September 2021