A von Willebrand factor (vWF) activity – ristocetin cofactor test lets you evaluate the functioning of the protein vWF, which helps blood to clot. A clot is a lump of blood that the body produces to prevent excessive bleeding by sealing leaks from blood vessels caused by wounds, cuts, scratches, or other conditions.
The blood’s ability to clot is a complex process involving platelets (also called thrombocytes) and proteins called clotting factors. Platelets are oval-shaped cells made in the bone marrow. Most clotting factors are made in the liver. Some, like vWF, are made in blood vessel walls.
When a blood vessel breaks, platelets are first to the area to help seal the leak and temporarily stop or slow bleeding. But for the clot to become strong and stable, the action of clotting factors is required.
The body’s clotting factors are numbered using the Roman numerals I through XII. They work together in a specialized sequence, 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, the puzzle can’t come together.
Von Willebrand factor is involved in the early stages of blood clotting. As the platelets gather at the injury site, vWF acts like glue, helping them stick together to stop the bleeding. Sometimes, though, children are born with an abnormal gene that causes them to produce too little vWF, or a defective version of it. The result is a bleeding disorder called von Willebrand disease.
Variations of von Willebrand disease range from mild to severe. In most cases, the genetic mutation that causes the disease is hereditary, but it may occur spontaneously as well.
Von Willebrand Disease Types:
Type 1: The most common type of VWD. There is not enough VWF in the bloodstream.
Type 2: The next most common type of VWD. There may be enough VWF, but it does not work correctly. VWF is made of long strands called multimers. In type 2 VWD, there may be a problem with the multimers working correctly.
Type 2A: VWF does not form the correct multimers and does not stick to the platelets.
Type 2B: VWF multimers stick too tightly to the platelets, which causes the body to get rid of the platelets with the VWF. This results in a low level of platelets and VWF that doesn’t work correctly.
Type 2M: VWF multimers are normal, but VWF is not able to stick to the platelets.
Type 2N: VWF cannot carry factor VIII normally and this causes low factor VIII levels.
Type 3: The rarest form of VWD. There is little or no VWF in the blood. This type is the most severe form of the disease with little to no VWF and low factor VIII levels.
Von Willebrand Disease Symptoms:
- Easy bruising
- Frequent nose bleeds
- Bleeding after dental work
- Bleeding following a surgery or procedure
- Heavy menstrual periods
- Less common is bleeding in the joints or muscles
von Willebrand Factor Activity
Every lab result you’ve ever had, charted and explained.
Healthmatters is a tracker for your lab results. Upload a report from any lab, any country — every marker charted and explained.
Start with my report →
All our content is backed by peer-reviewed studies, academic research, and trusted medical sources. We’re committed to accuracy and transparency — see our editorial policy for details.