At a Glance
Why Get Tested?
To help determine the cause of excessive or episodic bleeding, to diagnose von Willebrand's disease (vWD), and to distinguish between different types of vWD
When to Get Tested?
When you have a personal or family history of heavy, prolonged, and/or spontaneous bleeding; when your doctor suspects you may have a bleeding disorder
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
Von Willebrand factor (vWF or VWF) testing measures the quantity and/or function of von Willebrand factor. VWF is a protein and is one of several components that work together, and in sequence, to stop bleeding. Normally, when a blood vessel is damaged, VWF forms an adhesive bridge between activated cell fragments called platelets and the injury site. This is followed by the clumping (aggregation) of platelets at the site and a series of actions referred to as activation of the coagulation cascade, resulting in the formation of a stable blood clot. VWF further affects clotting by influencing the availability of coagulation factor VIII. VWF carries factor VIII in the blood, increases its half-life, and releases it as necessary. If there is not enough functional VWF, then platelet adherence and aggregation are compromised, levels of factor VIII could be decreased, blood clot formation takes longer, and therefore bleeding is prolonged. This results in a condition referred to as von Willebrand's disease (VWD).
VWD is the most common inherited bleeding disorder. It is a group of conditions associated with prolonged bleeding due to deficient and/or defective VWF. VWD is separated into different types and sub-types, including:
- Type 1 – with this type of VWD, there is a decrease in the amount of VWF produced, but the VWF functions normally. Levels of factor VIII are also typically low but may be normal. This is the most common type of VWD, accounting for about 75% of cases. It tends to cause bruising and mild to moderate bleeding, such as persistent nosebleeds, heavy menstrual periods, and prolonged bleeding following childbirth, trauma, dental procedures, and surgeries. Symptoms and the severity of bleeding will vary from person to person and from episode to episode.
- Type 2 – this type is associated with a normal amount of VWF, but the VWF does not function normally. Bleeding may be more severe with this with this type. Type 2 is further divided into Types 2A, 2B, 2M, and 2N.
- Type 3 – this rare type is associated with little to no VWF production, very low factor VIII levels, and moderate to severe symptoms. It is often detected in infancy because of early bleeding episodes.
Rarely, VWD may be due to an acquired VWF deficiency, where there is no family or personal bleeding history up to the point of presentation. It is sometimes seen in patients with:
- Conditions that cause the breakdown of VWF, such as pulmonary hypertension and structural defects of the heart (such as aortic valve stenosis)
- Lymphoma, myeloma, or autoimmune disorders (such as systemic lupus erythematosus) that cause the production of VWF antibodies
- Myeloproliferative neoplasms associated with increased platelet production that cause increased platelet binding
- Hypothyroidism, which can decrease VWF production
- Wilms tumor and other disorders that bind to VWF and remove it from the blood
- Certain medications such as valproic acid, ciprofloxacin, hetastarch
Von Willebrand factor tests include VWF antigen, which measures the amount of VWF, and VWF activity (also known as Ristocetin Cofactor), which evaluates the function of VWF. Some laboratories may offer a panel that includes both of these tests along with a factor VIII activity test.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
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