von Willebrand factor antigen (VWF:Ag)
- Description
- von Willebrand disease (VWD) can be sub-typed into quantitative (types 1 & 3) or qualitative (type 2) deficiencies. Types 1 & 3 involve a reduced concentration of normally functioning von Willebrand factor (VWF) or absent VWF, whilst type 2 involves dysfunctional molecules but normal or at least higher concentration compared to activity. Concentration of VWF irrespective of function is ascertained with a latex immunoassay which employs latex particles coated with antibodies to VWF to capture VWF in the test plasma. The VWF acts as a bridge between latex particles that leads to a degree of agglutination directly proportional to VWF concentration, which is measured turbidimetrically.
- Clinical details
- von Willebrand factor (VWF) is a large adhesive glycoprotein synthesised in endothelial cells and megakaryocytes. Unlike the activated coagulation factors of secondary haemostasis it is not an enzyme and its functions involve binding to cells and molecules. Upon vessel injury, VWF binds directly to exposed sub-endothelial collagen and remains anchored. Blood flow unravels anchored VWF to expose the binding site for the constitutively expressed platelet surface receptor glycoprotein Ib. VWF captures and tethers platelets arriving at the scene which promotes subsequent events of primary haemostasis towards formation of a platelet plug. VWF also serves as the plasma carrier of FVIII to protect it from proteolytic degradation and also to ‘deliver' it to sites of injury and clot formation. von Willebrand disease (VWD) is the most common hereditary bleeding disorder and the deficiency can be quantitative, involving reduced levels of normally functioning VWF, or qualitative, involving dysfunctional molecules. Laboratory investigation of VWD encompasses a battery of assays that assess different aspects of the molecule which inform sub-classification and clinical management: VWF:RCo assay measures glycoprotein Ib binding VWF:Ag assay measures total protein concentration irrespective of function VWF:CB assay measures collagen binding VWF:FVIIIB assay measures FVIII binding Multimer analysis investigates VWF structure FVIII activity is measured as levels can be reduced due to reduction of its carrier.
- Related condition
- Reference range
- Blood group O 50 - 124 Non-O blood groups 67 - 172
- Units
- IU/dl
- Testing site
- Synnovis : Blood Sciences : St Thomas' Hospital
- Laboratory
- Diagnostic Haemostasis and Thrombosis
- Sample type and volume required
- External requests: Citrated platelet poor plasma 350µL x 1 aliquot Internal requests: please refer to EPR label
- Special sample instructions
The sample should be analysed or manipulated & stored in the laboratory within 4 hours of venepuncture. Please ensure sample tubes are filled exactly to the fill-line as underfilling creates a dilution error and leads to inaccurate results.
- Turnaround time
- 5 - 7 days
- Contacts
Diagnostic Haemostasis and Thrombosis Department
St Thomas’ Hospital
Phone: 020 7188 2797
St Thomas’ Hospital
North Wing – 4th and 5th Floors
Westminster Bridge Road
London SE1 7EHGuy’s Hospital
Phone: 020 7188 7188 ext. 53860
Guy’s Hospital
Southwark Wing – 4th Floor
Great Maze Pond
London SE1 9RT
Outside core hours, contact Duty Haemostasis Biomedical Scientist