Click here for more information about laboratory operations and procedures
If you have additional questions regarding this test, please call: 415-353-1667
von Willebrand Factor Antigen
|Clinical Questions||Does my patient have von Willebrand disease? If so, which type?|
|Test group||von Willebrand|
|Performed by||Parnassus Hematology|
|Collection Instructions||1. Check the expiration date on the label of the blue top vacutainer before drawing the patient.
2. For blood collection in a sodium citrate blue top, the tube must be filled to above the Minimum Fill Indicator on the tube. It is crucial to wait and allow the tube to stop filling before removing it from the needle.
3. With use of a butterfly needle, draw about 1 cc using a separate blue top to remove air from tubing, discard the first tube and then draw a second blue top tube filled to the full extent of the vacuum.
4. Tubes should not be filled past the Maximum Fill dashed line by either using a syringe or removing the tube cap.
For patients with Hct's ≥ 55% please contact Hematology (415-353-1747) to obtain blue top tubes with adjusted citrate volumes in order to maintain the proper citrate to plasma ratio for coagulation studies.
|Container type||Blue top filled to full extent of vacuum|
|Amount to Collect||2.7 mL blood|
|Sample type||Citrated plasma|
|Preferred volume||1 mL plasma|
|UCSF Rejection Criteria||Samples collected in outdated blue top vacutainer. Over-filled or under-filled tubes may be rejected|
|Processing notes||If this test is ordered with Factor VIII Activity and Ristocetin Cofactor on the same sample, enter VWP to request all three tests.|
See Additional Information
|Synonyms||VWF:Ag; Factor VIII-Related Antigen; FVIII:RAg; FVIII:VWAg; VWAG; VW; VWF Antigen; vwd|
|Turn around times||Test run q1-2 weeks. Turnaround time: 3-10 days|
|Additional information||During infancy, vWF Antigen values can be greater than those observed in adults. Nevertheless, a value of approximately 40% was noted as the lower limit of normal for full term infants from birth to 6 months. (Reference: Andrew M. et al. Blood 1987 70:165).
Asymptomatic abnormalities of von Willebrand factor are common. The reference interval for von Willebrand Factor Antigen is set such that 2.5% of people will be below the limit of the reference range. Approximately 1 in 8000 people have symptomatic von Willebrand disease (VWD), which is usually associated with mucocutaneous bleeding.
Von Willebrand Factor Antigen levels should be correlated with patient and family bleeding history, as clinically indicated. The Ristocetin Cofactor Assay can be useful for assessing von Willebrand Factor Activity.
The presence of rheumatoid factor may lead to an over-estimation of the vWF level. The extremely rare presence of anti-bovine and/or anti-rabbit antibodies in certain patients may lead to an over-estimation of the vWF level
|Last Updated||6/21/2016 13:53|