von Willebrand factor collagen binding activity (VWF:CB)
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. The majority of dysfunctional molecules can be identified with the ristocetin co-factor activity assay but the dysfunction in some rare sub-types involves collagen binding.
The VWF collagen binding assays (VWF:CB) assay is performed with an indirect ELISA. VWF in patient plasma is captured in microtitre plates coated with type III human collagen. Unbound material is then washed away and a solution of antibody to human VWF that is conjugated to an enzyme is added to ‘tag’ onto any captured VWF. Unbound conjugate is washed off and a substrate for the enzyme is added, the product of the enzyme-substrate reaction being coloured. Colour intensity is in direct proportion to the degree of conjugate-binding, itself proportional to the amount of VWF capture and thus, VWF collagen binding activity.
The VWF collagen binding assays (VWF:CB) assay is performed with an indirect ELISA. VWF in patient plasma is captured in microtitre plates coated with type III human collagen. Unbound material is then washed away and a solution of antibody to human VWF that is conjugated to an enzyme is added to ‘tag’ onto any captured VWF. Unbound conjugate is washed off and a substrate for the enzyme is added, the product of the enzyme-substrate reaction being coloured. Colour intensity is in direct proportion to the degree of conjugate-binding, itself proportional to the amount of VWF capture and thus, VWF collagen binding activity.
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.
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 42 - 124
Non-O blood groups 59 - 147
Units:
IU/dl
Department:
Location:
Sample type and Volume required:
External requests: Citrated platelet poor plasma
400µL x 1 aliquot
Internal requests: please refer to EPR label
400µL x 1 aliquot
Internal requests: please refer to EPR label
Turnaround time:
7 - 10 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
St Thomas': 020 7188 2797; Guy's: 020 7188 7188 ext. 53860
St Thomas' Hospital
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH
Laboratory opening times
24/7
Guy's Hospital
Southwark Wing - 4th Floor
Great Maze Pond
London SE1 9RT
Outside core hours, contact Duty Haemostasis Biomedical Scientist
North Wing - 4th and 5th Floors
Westminster Bridge Road
London SE1 7EH
Laboratory opening times
24/7
Guy's Hospital
Southwark Wing - 4th Floor
Great Maze Pond
London SE1 9RT
Outside core hours, contact Duty Haemostasis Biomedical Scientist
Last updated: 09/03/2017
