von Willebrand factor ristocetin co-factor activity (VWF:RCo)

Description: 
von Willebrand disease (VWD) can be sub-typed into quantitative (types I & 3) or qualitative (type 2) deficiencies. Types I & 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.

The VWF ristocetin co-factor (VWF:RCo) assay is performed with a new generation automated assay employing latex beads coated with a recombinant fragment of GpIbα through a highly specific monoclonal antibody. VWF in the sample binds to the GpIbα fragment via the antibiotic ristocetin and the degree of agglutination is directly proportional to VWF (GPIb-binding) activity, determined by decreased light transmittance due to the agglutination.
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.
Reference range: 

Blood group O 41 - 107
Non-O blood groups 58 - 127

Units: 
IU/dl
Sample type and Volume required: 
External requests: Citrated platelet poor plasma
350µL x 1 aliquot
Internal requests: please refer to EPR label

Turnaround time: 
5 - 7 days
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.

Contacts:
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
24/7
For clinical advice or interpretation of results, please contact the laboratory in the first instance.

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Last updated: 09/03/2017