At a glance
Also known as
VWF:Ag; VWF:RCo; von Willebrand Panel; Ristocetin Cofactor; Collagen binding
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?
There are a number of dietary factors such as caffeine and lifestyle factors such as stress or pregnancy that influence the test results. Preparation instructions are given before a test sample is collected.
What is being tested?
Von Willebrand factor (vWF or VWF) testing measures the quantity and function of von Willebrand factor. VWF is a blood-clotting and one of several components that work together and in sequence to stop bleeding by forming a blood clot. Normally, when a blood vessel is damaged, VWF first forms an adhesive bridge between blood platelets and the injury site. Next, it enables the platelets to clump together. Then follows a series of actions that are referred to as 'activation of the coagulation cascade'. VWF further helps clotting through another protein, coagulation factor VIII. VWF carries factor VIII in the blood, increases its , and releases it as necessary. If there is not enough functional VWF, platelet adherence and aggregation are compromised, levels of factor VIII can be decreased, blood clot formation takes longer, and bleeding is prolonged. This results in a condition referred to as von Willebrand's disease (VWD).
VWD is the most commonly inherited bleeding disorder. It is a group of conditions associated with prolonged bleeding due to deficient and/or defective VWF. VWD is separated into six 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 per cent of cases. It tends to cause bruising and mild to moderate bleeding; examples include, persistent nosebleeds, heavy menstrual periods and prolonged bleeding following childbirth, trauma, dental and surgical procedures. Symptoms and the severity of bleeding 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 subdivided 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
- Myeloproliferative disorders associated with increased platelet production that cause increased platelet binding
- Hypothyroidism, which can decrease VWF production
- Wilms tumour and other disorders that cause VWF to be removed from the blood
- Certain medications such as valproic acid, ciprofloxacin, hetastarch
There are a number of different tests to help confirm a diagnosis of VWD. Most laboratories offer only some of these tests. Your diagnosis may need to rely on tests obtained from different laboratories.
In order to make a diagnosis of VWD your doctor will select the appropriate tests based on your bleeding history. Different tests are influenced by factors such as age, ethnicity, blood type and diet at the time of testing, as well as environmental influences. It is not uncommon for someone to require many repeated tests before a diagnosis is made due to the many variables affecting test results.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
There are a number of dietary factors such as caffeine, as well as lifestyle factors such as stress or pregnancy that influence the test results. Preparation instructions are given before a test sample is collected.