What are the other Names for this Test? (Equivalent Terms)
- von Willebrand Panel of Antigen Level & Factor Activity
- vWF: Ag Level with Activity
What is von Willebrand Factor Antigen & Activity Test? (Background Information)
- Von Willebrand disease (vWD) is a most common type of inherited bleeding disorder.Infrequently, vWD can be sporadic, occurring without any family history
- In this disorder, a protein called von Willebrand factor (vWF) is either defective or is present in low levels in the body. The von Willebrand factor is an important protein, which is critically needed for blood to clot, following an injury
- The protein helps in clumping together the platelets in the body, to form a blood clot. Blood clots plug an area of bleeding, when a blood vessel is damaged
- The von Willebrand factor is manufactured in cells in the bone marrow, called the megakaryocytes, and also by the endothelial cells, which form the blood vessels lining. The megakaryocytes make the platelets and vWF are released as part of the platelets. The endothelial cells release vWF, whenever the blood vessels are damaged
Two tests, namely the von Willebrand Factor Antigen Blood Level and the von Willebrand Factor Activity, together helps in the diagnosis of vWD. This test is usually performed in association with other tests, such as platelet count, platelet function tests, CBC, coagulation Factor VIII, PT (prothrombin time) and PTT (partial thromboplastin time).
- The von Willebrand Factor Antigen level determines the amount of the protein in the blood. The von Willebrand Factor Activity determines the function of the protein
- One may have a normal level of the protein, but the activity may be decreased, resulting in von Willebrand disease (vWD). There are three types of von Willebrand disease, classified as type 1, type 2, and type 3
- vWD is not hemophilia. In hemophilia, a protein called ‘Factor VIII’ is either defective (due to improper functioning) or present in low levels. The severity of hemophilia depends on the levels of Factor VIII; lower the level, the more severe is the disease
- In normal healthy conditions, the Factor VIII is bound to vWF (physiologically) and hence, testing for bleeding disorder includes an analysis for both levels, to determine which protein is the cause of bleeding disorder
- Von Willebrand disease can affect both male and females. However, hemophilia is commonly seen in males, because of its X-linked inheritance pattern
What are the Clinical Indications for performing the von Willebrand Factor Antigen & Activity Test?
- The von Willebrand Test is indicated when your healthcare provider suspects a bleeding disorder
- This test is also performed when one has a family history of bleeding disorder, such as von Willebrand disease or hemophilia
- Sometimes, the test is also performed when other tests done to determine the bleeding and clotting process in the body, indicates a bleeding disorder through abnormal test results
Such abnormal tests may include:
- CBC (complete blood count)
- Platelet count
- Platelet function tests (such as abnormal platelet aggregation studies)
- PT (prothrombin time)
- PTT (partial thromboplastin time)
How is the Specimen Collected for von Willebrand Factor Antigen & Activity Test?
Sample required: Blood
Process: Insertion of the needle into a vein (arm).
Preparation required: None
What is the Significance of the von Willebrand Factor Antigen & Activity Test Result?
- A trained healthcare provider in hematological bleeding disorders should interpret an abnormal von Willebrand Factor Antigen and Von Willebrand Factor Activity Test results
- There are different types of von Willebrand disease. Each type has a different profile of von Willebrand Factor Antigen level and von Willebrand Factor Activity
- In individuals with mild forms of von Willebrand disease, the von Willebrand Factor Antigen level and von Willebrand Factor Activity may be completely normal
- An increased von Willebrand Factor Antigen level and an increased von Willebrand Factor Activity can be seen in individuals, who do not have von Willebrand disease. This is because vWF is a type of acute phase reactant, which is increased in many conditions. Conditions, which may increase von Willebrand Factor, include:
- A variety of infections
- Increased acute and chronic inflammation, due to autoimmune disorders
- Intense exercising
- Emotional stress
- Physical trauma to the body
- Heart defects, such as aortic stenosis
- Infarction (anywhere in the body)
- Various types of neoplasms such as leukemias, lymphomas, and myelodysplastic syndromes
If von Willebrand Factor Antigen level and von Willebrand Factor Activity is abnormal, then further work-up is necessary. The follow-up tests may include:
- Ratio of vWF: RCo to vWF: Ag – this test determines the ratio of how well the von Willebrand factor functions in the body, given the amount of vWF in your blood
- Factor VIII antigen levels and binding (clotting) activity assay – this test determines the clotting activity of Factor VIII
- Platelet vWF aggregation studies help in determining how well the platelets are functioning
- Ristocetin-induced platelet aggregation (RIPA) or platelet-binding, helps determine how well the platelets are functioning
- vWF propeptide (vWFpp) to vWF antigen ratio
- Molecular genetic testing for vWD (to determine the subtype, namely Type 2N and Type 3)
- Multimeric analysis – this test helps in determining the type of vWD. vWF is a complex protein structure that exists as "multimers" of different size and shapes. This test looks at the distribution of different sizes to help distinguish between Type 2 subtypes
- Collagen binding activity assay
Sometimes the initial screening test may be normal. If the clinical suspicion of a bleeding disorder is high, then the tests may have to be repeated.
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Additional and Relevant Useful Information:
- It is important to note that the vWF concentrations in blood may be affected if the individual has ABO blood type
- It has been found that individuals with type O blood have lower vWF levels. This level can be as low as 25%, when compared to blood groups type A, B, and AB
- An Rh factor, does not affect the level of vWF concentrations in blood
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.