von Willebrand factor ristocetin cofactor (VWF:RCo) assay: implementation on an automated coagulometer (ACL)

Abstract

Summary. Background: VWF:RCo assay is the standard and widely used laboratory test for von Willebrand disease (VWD) diagnosis. It is hampered by high intra‐ and inter‐assay imprecision and is time consuming. Automation may improve the assay performance and allow its routine application. Objective: Automation of VWF:RCo on the ACL 7000 coagulometer (Instrumentation Laboratory, Milan, Italy) and its evaluation in VWD diagnosis. Methods and materials: Method performance determination: precision, detection limit (DL), interferences, dose–response curve. Method comparison: analysis of 105 plasma samples from normal subjects (50), VWD type 1 (24), VWD type 2 (24) and VWD type 3 (7) with ACL VWF:RCo and comparison with the reference aggregometric (AGM) method. Results: ACL VWF:RCo: CVs around 10% vs. 19% of AGM method; DL: 0.08 U mL−1; potential interferences from bilirubin, triglycerides and hemoglobin, avoided by suitable plasma dilution; high correlation with AGM VWF:RCo (Deming regression Y =−0.0277 + 1.0519X) either in normal or VWD plasmas. In VWD types 1 and 2, the VWF:RCo/VWF:Ag ratios are >0.6 or <0.6, respectively, when calculated with both AGM and ACL VWF:RCo values. Conclusions: The automated VWF:RCo on the ACL 7000 coagulometer shows precision improvement and high correlation with the reference AGM method. The test allows the diagnosis of both quantitative (VWD types 1 and 3) and qualitative (VWD type 2) forms of the disease. These results and the assay feasibility make it a suitable and reliable test for the routine diagnosis of VWD.

Improved performance characteristics of the von Willebrand factor ristocetin cofactor activity assay using a novel automated assay protocol

“…This assay has been shown to have a high variability depending on the reagents and standards used, which makes it less reliable as well as labor and cost intensive [9][10][11]. Thus, in recent years, several fully automated VWF:RCo assay protocols have been described [11][12][13][14][15]. They allow greater throughput of samples with improved analytical precision compared with manual and semi-automated assays.…”

Comparison of several von Willebrand factor (VWF) activity assays for monitoring patients undergoing treatment with VWF/FVIII concentrates: improved performance with a new modified automated method

“…However, these have not been widely accepted for therapeutic or diagnostic practice because of their non-functional nature and their inability to differentiate some of the VWD subtypes. One of the major advantages of fully automated VWF:RCo methods compared with semi-automated and manual methods is greater throughput of samples with better analytical precision [8][9][10][11][12]. Disadvantages include high LODs, underestimation of VWF:RCo activity due to polymorphisms affecting the ability of ristocetin to bind VWF, reagent variability between lots as well as the possibly of calibration error, and variable results reflecting the intrinsic imprecision in these methods.…”

“…The semi-automated VWF:RCo assay exhibits high variability depending on the reagents and standard used [5,7,[13][14][15]. Automated VWF:RCo assays are easier to perform, allow greater throughput of samples with greater analytical precision, and can generate assay results with a faster turnaround time [8][9][10][11][12]. Furthermore, automated VWF:RCo assays are less labour-and reagent-intensive compared with manual and semi-automated assays, resulting in greater cost effectiveness.…”

Diagnosis and classification of von Willebrand disease

“…Historically, VWF:RCo was first utilized as an agglutination assay primarily in platelet aggregometers or using a manual visual slide agglutination procedure; both of these methods are laborious. VWF:RCo by platelet agglutination has also been successfully automated on many modern haemostasis analysers, including the Siemen's BCS, IL ACL instrumentation, Stago STAR and most recently the Sysmex CA-2000i/CA2100i instruments [41][42][43][44][45][46][47][48]. Methods for VWF:RCo based on flow cytometry have also been described [49,50], as have ELISA-based methods [51][52][53].…”