title: Evaluation of a rapid automated assay for analysis of von Willebrand ristocetin cofactor activity.
abstract: A commercially available turbidometric assay has been evaluated for the measurement of von Willebrand factor ristocetin cofactor activity (VWF:RCo). The assay is simple, rapid, and can be cost-effectively performed on automated coagulation analyzers. This study's aim is to illustrate the performance of the automated VWF:RCo assay and its capacity to identify patients with von Willebrand disease (VWD). By direct comparison with a conventional VWF:RCo assay, performed on an aggregometer, the concordance between the two assays was 96%. With minor modifications, the automated assay showed a detection level of 0.03 kIU/L with linearity to 2.00 kIU/L. The imprecision of the automated assay was reduced compared to the conventional assay procedure with CV of 6.8% at the 1.00 kIU/L level and 8.6% at the 0.30 kIU/L level. The automated VWF:RCo assay was also suitable as a screening test to detect VWD in patients investigated for the cause of an increased bleeding tendency. In this situation the automated VWF:RCo assay was tested simultaneously with an automated immunoassay for von Willebrand antigen. Receiver operating curves for the diagnosis of VWD showed a greater area under the curve for the automated VWF:RCo assay compared to the immunoassay, 0.98 vs. 0.94, although the difference did not reach significance. In conclusion, the modified automated VWF:RCo assay shows better precision, lower detection limit, is faster to perform with a lower cost per test compared to the conventional aggregometer based VWF:RCo activity method and is an alternative to an antigen immunoassay as a screening test for VWD.
authors.affiliation: Department of Coagulation Disorders, Lund University, Malmö University Hospital, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Strandberg
authors.forename: Stefan
authors.initials: S
authors.lastname: Lethagen
authors.forename: Kerstin
authors.initials: K
authors.lastname: Andersson
authors.forename: Margareta
authors.initials: M
authors.lastname: Carlson
authors.forename: Andreas
authors.initials: A
authors.lastname: Hillarp
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001331:Automation; D001780:Blood Coagulation Tests / Q000592:standards; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry; D012372:ROC Curve; D013997:Time Factors; D014842:von Willebrand Diseases / Q000175:diagnosis*; D014841:von Willebrand Factor / Q000032:analysis*
chemical_list: D014841:von Willebrand Factor