Background: Von Willebrand disease (VWD) diagnosis and classification usually require a combination of nonspecific and VW-factor (VWF)-specific assays. We evaluated the analytical performance of a commercially available collagen-binding assay (CBA) and its usefulness in conjunction with other assays for laboratory diagnosis of VWD.
Methods: We used a commercial CBA ELISA (Life Technologies) to evaluate 3085 plasma samples. We used standard procedures to perform other assays, including factor VIII activity (FVIII:C), VWF antigen (VWF:Ag), ristocetin cofactor activity, VWF collagen binding capacity (VWF:CB), and VWF multimeric analysis.
Results: CBA intra- and interassay CVs were <6% and <13%, respectively. Reference intervals were 45%-198% for VWF:CB and 0.75-1.32 for the VWF:CB/Ag ratio. Of 3085 samples tested, 235 (8%) had results commonly associated with VWD. Multimer analysis and phenotypic data in 156 samples identified VWD types as: 91 (58%) type 1, 62 (40%) type 2, and 3 (2%) type 3. Of the 91 type 1 samples, proportional decreases in functional activity were seen in 75 samples (82%) according to CBA and in 63 samples (69%) according to the ristocetin cofactor assay. Of the type 2 samples, 10 were further identified as probable type 2A, 26 as probable type 2B, 12 as probable type 2M, and 14 could not be subtyped. VWF:CBA/Ag ratios <0.5 occurred in 83% of VWD type 2A and 2B samples, indicating characteristic functional discordance. Mean (SD) VWF:CB values were significantly higher in individuals without group O blood [113 (45)] than in those with group O blood [83 (32)] (t-test, P = 0.007).
Conclusions: The commercial CBA assay produces reliable results and is useful for laboratory diagnosis of VWD.