Use of the collagen-binding assay for von Willebrand factor
in the analysis of type 2M von Willebrand disease:
a comparison with the ristocetin cofactor assay

Authors

  • Anne F. Riddell,

    1. Katharine Dormandy Haemophilia Centre and Haemostasis Unit, Department of Haematology, Royal Free Hospital, Pond Street, London NW3 2QG, UK
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  • P. Vincent Jenkins,

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    • *

      Present address: Department of Biophysics and Biochemistry, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.

  • Ioana C. Nitu-Whalley,

    1. Katharine Dormandy Haemophilia Centre and Haemostasis Unit, Department of Haematology, Royal Free Hospital, Pond Street, London NW3 2QG, UK
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  • Angus H. McCraw,

    1. Katharine Dormandy Haemophilia Centre and Haemostasis Unit, Department of Haematology, Royal Free Hospital, Pond Street, London NW3 2QG, UK
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  • Christine A. Lee,

    1. Katharine Dormandy Haemophilia Centre and Haemostasis Unit, Department of Haematology, Royal Free Hospital, Pond Street, London NW3 2QG, UK
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  • Simon A. Brown

    1. Katharine Dormandy Haemophilia Centre and Haemostasis Unit, Department of Haematology, Royal Free Hospital, Pond Street, London NW3 2QG, UK
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: Professor Christine A. Lee, Haemophilia Centre and Haemostasis Unit, Royal Free and University College Medical School, Pond Street, London NW3 2QH, UK. E-mail: Christine.Lee@ rfh.nthames.nhs.uk

Abstract

Summary. This study compares the utility of two functional assays for von Willebrand factor (VWF), the ristocetin cofactor assay (VWF:RCo) and the collagen-binding assay (VWF:CBA). We analysed a group of 32 patients with type 2 von Willebrand disease (VWD) (25 patients with type 2M, six with type 2A and one with type 2B) and 22 normal control subjects. VWF:RCo/VWF antigen (VWF:Ag) ratios and VWF:CBA/VWF:Ag ratios were compared between the patient and control groups. In the six patients with type 2A VWD, both VWF:RCo/VWF:Ag ratios and VWF:CBA/VWF:Ag ratios were discordant (≤ 0·7). In the 25 type 2M VWD patients, the VWF:CBA/VWF:Ag ratios were concordant (> 0·7), but the VWF:RCo/VWF:CBA ratios were discordant (≤ 0·7) (P = 0·001) compared with control subjects. Thus, VWF:RCo/VWF:Ag ratios were discordant in both type 2M and 2A VWD patient groups indicating a functional abnormality. However, VWF:CBA/VWF:Ag ratios were discordant in the type 2A VWD group but not in the type 2M VWD group. Our study showed that VWF:CBA is sensitive to functional variants associated with the loss of high-molecular-weight multimers, i.e. type 2A and 2B in VWD, but the assay was unable to discriminate defective platelet-binding VWD variants with normal multimeric patterns such as type 2M VWD. It was concluded that the VWF:CBA assay should be used in association with rather than as a replacement for the VWF:RCo assay.

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