Testing for VWD
Some people may have VWD for years and never know that they have it. This may be because they do not have symptoms or their symptoms are very mild. This can be especially true for men. They might only be diagnosed when having surgery or if a woman in their family is diagnosed.
Other people may not be diagnosed because their doctors do not know about VWD. Their symptoms might be ignored or believed to be caused by something else. This is particularly common in teen girls and women with heavy periods.
Testing for VWD is best done by a specialist in bleeding disorders, such as the hematologist at a hemophilia treatment center (HTC). He or she will know how to perform and interpret the tests accurately.
Your medical history is as important to the doctor as the laboratory tests. The doctor will want to know:
- when you first began having the symptoms of bleeding
- the parts of your body that you bleed from
- how the bleeding starts and how long it lasts
- what was done to stop the bleeding
- how often the bleeding happens
- if other people in your family have had problems with bleeding
Testing can be difficult
Testing for VWD, especially Type 1, can be difficult because the level of VWF can be easy to raise temporarily. Some of the things known to affect VWF levels are:
- Pregnancy – VWF levels rise during pregnancy.
- Estrogen and some birth control pills – These can raise the VWF level in the blood.
- Stress – Stress increases the amount of VWF in the blood. This stress can be as simple as being nervous or crying when having blood drawn. This can make VWD testing very difficult in children.
- Exercise – Exercise raises the VWF level in the blood.
- Infection – Having an active infection can increase the VWF level.
A person’s blood type can also affect his or her VWF level. People with type O blood have lower levels of VWF than people in blood groups A, B, and AB. Your blood type may be important for the doctor to know when interpreting the VWD test results.
Problems with your thyroid gland can make VWF levels go up or down. The doctor might test your thyroid to make sure it is not the cause of your symptoms.
Blood Tests for VWD
The doctor will order several blood tests to check for VWD. This is necessary because of the different types of the disorder. Because so many things affect the VWF level, it may be necessary to do the tests more than once. Some of the blood tests used to diagnose VWD are:
- Von Willebrand Factor Antigen – This test measures how much VWF is in the blood. It does not tell how well the VWF functions.
- Ristocetin Cofactor Assay – Normal platelets and the antibiotic ristocetin are added to the tube of plasma from the person being tested. A machine measures how well the platelets stick together. This is one of the tests for measuring how well your VWF works (it’s function or activity). It should be ordered with the VWF Antigen test.
- Von Willebrand Factor Multimers – This test measures the different parts of the VWF protein. This can help determine which type of VWD someone has. It is typically done only after someone is confirmed to have VWD.
- Factor VIII level – This test measures how much factor VIII is in the blood. Since VWF is a carrier of factor VIII, a low VWF level can also cause a low factor VIII level. However, most people with VWD will have a normal or low normal factor VIII level.
- Bleeding Time or Platelet Function Analyzer (PFA 100®) – The bleeding time is not a recommended test for VWD since many people with the condition will have a normal test result. It can also cause a scar on the skin. Testing with the PFA 100® is sometimes used to screen for bleeding problems but it can’t diagnosis VWD. The PFA 100® result may be abnormal in VWD but may also be abnormal if there is a platelet dysfunction or anemia.
- Collagen Binding Assay – This test measures the binding of the VWF to collagen, one type of protein in the body. It is another test of the VWF function.