Development of an ELISA method for testing VWF ristocetin cofactor activity with improved sensitivity and reliability in the diagnosis of von Willebrand disease

Objectives: Current methods in assessing von Willebrand factor (VWF) ristocetin cofactor activity for Von Willebrand’s disease (VWD) diagnosis include platelet agglutination by aggregometer or macroscopic slide examination, which are both time‐consuming with suboptimal interassay and intra‐assay variation. The purpose of this study is to establish a sensitive assay to detect VWF:RCo activity and evaluate its performance in VWD diagnosis. Methods: We have established a sensitive VWF:RCo–ELISA method using a monoclonal antibody, SZ‐151, to immobilize the recombinant fragment of platelet glycoprotein Ib (rfGPIbα). VWF was captured by rfGPIbα in the presence of ristocetin, and then detected by HRP‐conjugated rabbit anti‐human VWF IgG. We tested the VWF:RCo level by this VWF:RCo–ELISA in 25 patients with different types of VWD and 36 healthy donors, and compared this method to a previously reported ELISA using 2D4 coating antibody. Results: The sensitivity of VWF:RCo–ELISA was greatly improved with this assay (0.008 IU/dL compared to 0.031 IU/dL by 2D4 antibody). The interassay and intra‐assay coefficient variation were 8% and 12%, respectively. The mean values (ranges) of VWF:RCo in patients with type 1, type 2A, type 2B, type 2M, and type 3 of VWD and control group are 31.8 (22.3–56.9), 4.8 (0.6–11.8), 8.6 (1.6–19.7), 3.9 (1.0–6.8), 1.0 (0.5–1.6), and 91.5 (47.3–169.2) IU/dL, respectively. The corresponding ratios (ranges) of VWF:RCo / VWF:Ag are 0.83 (0.70–1.16), 0.27 (0.08–0.58), 0.31 (0.15–0.40), 0.18 (0.14–0.21), 0.52 (0.13–1.19), and 0.92 (0.62–1.26). Conclusion: The VWF:RCo–ELISA using monoclonal anti‐rfGPIbα antibody SZ‐151 showed improved sensitivity and reliability in detecting VWF:RCo activity, and its clinical application would facilitate the diagnosis and classification of VWD.