title: A rapid, automated VWF ristocetin cofactor activity assay improves reliability in the diagnosis of Von Willebrand disease.
abstract: BACKGROUND
  The effective diagnosis and monitoring of Von Willebrand Disease (VWD) requires an accurate assessment of ristocetin co-factor activity (VWF:RCo). 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
  We have evaluated an automated VWF:RCo 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 VWF:RCo assay. Good correlation was found between the two assays (r=0.91) in 53 patients with VWD. The mean manual VWF:RCo was 0.25IU/ml and mean automated VWF:RCo was 0.27IU/ml. A comparable increase in VWF:RCo following treatment, mostly with Desmopressin, was found in 13 patients with type 1 VWD (mean 3.9 fold increase with manual VWF:RCo and 3.1 fold with the automated VWF:RCo). In 13 patients with type 2 or 3 VWD following treatment mostly with concentrate , a higher increase was found with the automated VWF:RCo assay than the manual assay (mean 11.9 fold manually and mean 20.3 automated).
  
  
  CONCLUSIONS
  The automated VWF:RCo 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.
authors.affiliation: Sheffield Haemophilia and Thrombosis Centre, Sheffield, UK. Annette.bowyer@sth.nhs.uk
authors.forename: Annette E
authors.initials: AE
authors.lastname: Bowyer
authors.forename: Fiona
authors.initials: F
authors.lastname: Shepherd
authors.forename: Stephen
authors.initials: S
authors.lastname: Kitchen
authors.forename: Michael
authors.initials: M
authors.lastname: Makris
mesh_terms: D001780:Blood Coagulation Tests / Q000191:economics / Q000379:methods; D001792:Blood Platelets / Q000166:cytology; D003894:Deamino Arginine Vasopressin / Q000627:therapeutic use; D006490:Hemostatics / Q000627:therapeutic use; D006801:Humans; D010974:Platelet Aggregation; D010979:Platelet Function Tests / Q000191:economics / Q000379:methods; D012310:Ristocetin; D013997:Time Factors; D014842:von Willebrand Diseases / Q000097:blood* / Q000175:diagnosis* / Q000188:drug therapy; D014841:von Willebrand Factor
chemical_list: D006490:Hemostatics; D014841:von Willebrand Factor; D012310:Ristocetin; D003894:Deamino Arginine Vasopressin