Platelet VWF:antigen

Platelets are concentrated, washed and then lysed with a detergent. VWF in the supernatant is measured with a latex immunoassay which employs latex particles coated with antibodies to VWF to capture VWF in the supernatant. 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. Some type 1 sub-types have reduced VWF in platelet α-granules and measurement can be useful. Measuring platelet VWF can be useful in detecting disorders of platelet α-granules.
Reference range: 

Under review

mg/dl 1012 plt
Sample type and Volume required: 
Contact laboratory.
Turnaround time: 
Contact laboratory
Special sample instructions: 

50 ml of blood is taken into specially prepared citrate/EDTA anticoagulant tubes and delivered directly to the laboratory for immediate manipulation.

Diagnostic Haemostasis and Thrombosis Department
020 7188 2797
St Thomas' Hospital
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH

Laboratory opening times
For clinical advice or interpretation of results, please contact the laboratory in the first instance.

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Last updated: 07/08/2015