Background: The collagen-binding assay, a functional assay of Von Willebrand factor (VWF), discriminates the subtypes of Von Willebrand disease (VWD). Commercial collagen binding assays have the advantage of immediate use for fast results, but are expensive.
Methods: In this study we evaluated an in-house collagen-binding assay using type III collagen. We included it in the diagnostic work-up of 44 patients with VWD and 40 normal subjects. Other assays included VWF antigen, ristocetin cofactor activity, ristocetin-induced platelet agglutination and VWF multimeric analysis.
Results: The cost of this collagen-binding assay is 10-fold lower than that of commercial kits. The intra- and inter-assay coefficients of variation were <8% and <9% for normal values, respectively, and the normal reference range varies between 51% and 143%. This assay is sensitive to large VWF multimer representation, with a mean collagen-binding activity/antigen level (CB/Ag) ratio of 0.18 and 0.45 for type 2A and type 2B VWD, respectively, indicating functional discordance. It correlates with the antigen levels in type 2M and type 1 VWD, with mean CB/Ag ratios of 1.1 and 1, respectively.
Conclusions: Our cost-effective in-house collagen-binding assay produced reliable results. We recommend the use of this test together with the ristocetin cofactor test in the diagnostic work-up of VWD.