von Willebrand factor antigen test, von Willebrand factor activity test, ristocetin cofactor activity test, factor VIII coagulant activity test
This panel of tests is used to diagnose von Willebrand disease, a bleeding disorder that causes excessive bleeding from minor injuries or normal physical processes such as menstruation. It's the most common inherited bleeding disorder, but few people with the disease have symptoms.
If you have von Willebrand disease, you either don't have enough of a substance in your blood called von Willebrand factor, or your von Willebrand factor doesn't work the way it should. This substance plays several important roles in blood clotting, including helping platelets in the blood stick to each other and to the lining of your blood vessels.
This condition is inherited in three forms:
Type 1, in which you have too little of the von Willebrand factor
Type 2, in which the factor is defective
Type 3, in which the factor is completely missing
Sometimes people develop von Willebrand disease from medical reasons, although that condition is rarer than the inherited forms.
You may need the test for von Willebrand disease if you have symptoms of the condition:
Unusual bleeding from minor injuries
Unusual bleeding from your gums or nose
In women, abnormally heavy or lengthy periods
Abnormal bleeding after dental or medical procedures
Bleeding after taking nonsteroidal anti-inflammatory medications
You may also need this test if your health care provider notes that you have bleeding in your digestive tract or in your joints.
Bleeding can range from mild and occasional to life-threatening hemorrhages.
If your initial test results are unusually low or require additional information, your health care provider may order more specialized blood tests. These may include:
Von Willebrand factor multimer analysis. This test finds out if you have one of the subtypes of type 2 von Willebrand disease.
Ristocetin-induced platelet aggregometry. This finds out whether you have a form of type 2 disease or another disease that mimics von Willebrand disease.
Von Willebrand factor or factor VIII binding assay. This is another test for a form of type 2 disease.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
The initial lab tests to determine von Willebrand disease measure the following three substances from blood samples. Different measurements of these substances may tell which type of von Willebrand disease you have:
Von Willebrand factor antigen. This test measures your blood levels of von Willebrand factor.
Ristocetin-cofactor activity. This test measures how well your von Willebrand factor is working.
Factor VIII coagulant activity. Factor VIII is a protein in your blood carried by von Willebrand factor that plays a role in blood clotting.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Anxiety and stress can make your levels of von Willebrand factor and factor VIII go up. Exercising shortly before the test also can cause a rise in von Willebrand factor.
These are other things that can affect your results:
Difficulty drawing a blood sample
Certain illnesses that trigger inflammation in the body
Hormonal medications, including estrogen and birth-control pill
Try to remain calm before the blood test. Tell your health care provider if you're pregnant, if you have any medical conditions or illnesses, or if you have recently exercised. In addition, be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.