A rapid, automated VWF ristocetin cofactor activity assay improves reliability in the diagnosis of Von Willebrand disease.

ABSTRACT

INTRODUCTION: The effective diagnosis and monitoring of Von Willebrand Disease (VWD) requires an accurate assessment of ristocetin co-factor activity (VWFRCo). Current methodologies include automated platelet aggregometry and manual visual agglutination both of which are laborious to perform and notoriously subject to a high degree of inter and intra assay variation. METHODS AND MATERIALS We have evaluated an automated VWFRCo assay (BC Von Willebrand Reagent, Siemens, Marberg, Germany) for use on the Sysmex CS2100i analyser (Milton Keynes, UK) and retrospectively compared the results with an in-house manual visual agglutination assay and VWF antigen (Siemens) in normal subjects and in 53 patients with various types of VWD and 23 patients following VWF therapeutic treatment. RESULTS: The intra and interassay CV was improved with the automated assay (2.3% and 3.8% respectively) compared to 7% with the manual VWFRCo assay. Good correlation was found between the two assays (r=0.91) in 53 patients with VWD. The mean manual VWFRCo was 0.25IU/ml and mean automated VWFRCo was 0.27IU/ml. A comparable increase in VWFRCo following treatment, mostly with Desmopressin, was found in 13 patients with type 1 VWD (mean 3.9 fold increase with manual VWFRCo and 3.1 fold with the automated VWFRCo). In 13 patients with type 2 or 3 VWD following treatment mostly with concentrate , a higher increase was found with the automated VWFRCo assay than the manual assay (mean 11.9 fold manually and mean 20.3 automated). CONCLUSION: The automated VWFRCo assay shows enhanced precision and analysis time in this difficult and time consuming laboratory test and its introduction should greatly improve the reliability of VWF testing.