VWF:FVIII Binding Assay

Coagulation

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Description

One function of von Willebrand factor (VWF) is to bind clotting factor VIII (FVIII). This complex protects against proteolytic degradation of FVIII, and increases the half-life to approximately 12 hours. Type 2N (Normandy) von Willebrand disease (VWD) is a qualitative variant of VWF with a markedly decreased affinity for FVIIIbinding. In type 2N VWD, the VWF protein appears structurally normal but has reduced binding capacity for FVIII. This causes a decrease of FVIII because of a shortened half-life whereas VWF antigen (VWF:Ag) and VWF activity levels may be normal. Phenotypically, this mimics mild haemophilia A and may result in misclassification of patients.

In the VWF:FVIII binding assay, patient or control VWF binds to an anti-human VWF antibody that coats microtitre plate wells. Any endogenous FVIII that is bound to the VWF is removed with calcium chloride and exogenous recombinant FVIII is added. The VWF will bind FVIII according to its FVIII binding capacity. A secondary antibody will capture any bound FVIII and a chromogenic substrate is used to determine the degree of binding.

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Indications

Patients with a reduced FVIII activity as a differential diagnosis of mild haemophilia A or type 2N VWD.

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Sample Type

2 x 0.5ml aliquots of citrated plasma.

VWF:Ag level is required from the same venepuncture as the VWF:FVIIIB request. This can be provided by the requesting laboratory or performed within our laboratory.

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Reference Range

Results reported as normal or abnormal FVIII binding.

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Turnaround Time

Within 12 weeks

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Testing Frequency

As Required (usually batched four times per year). Abnormal results are repeated prior to reporting.

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External Notes

The accuracy of all coagulation tests is greatly influenced by pre analytical variables. It is essential that sample quality is given the highest of priorities. Samples which fail to meet quality criteria including age of sample, specimen fill (>90%), haemolysed, clotted or activated samples will be rejected and a repeat sample requested.

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Patient Preparation

No special requirements.

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References

Nesbitt IM et al (1996). Characterisation of type 2N VWD using phenotypic and molecular techniques. Thromb Haemost, 75(6), 959-964.

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Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.