title: Validation of automated latex von Willebrand factor activity assay in a new prospective study including post-treatment patient samples.
abstract: BACKGROUND
  Von Willebrand disease (VWD) is the most prevalent inherited bleeding disorder. Diagnosis requires measurement of VWF-platelet binding function, for which VWF ristocetin cofactor activity (VWF:RCo) is the reference method. Recently, an automated latex particle-enhanced immunoturbidimetric von Willebrand factor activity assay (VWF:Ab) has been validated showing superior characteristics. We further validate VWF:Ab in a prospective study including post-treatment patient samples.
  
  
  METHODS
  A total of 1151 samples were collected from patients tested for VWD, including 119 samples from patients treated with desmopressin or VWF replacement product. All samples were tested for VWF:Ab and VWF:RCo, and the methods were compared using linear regression. Imprecision, linearity and lower detection limit were determined for both assays.
  
  
  RESULTS
  VWF:Ab showed improved precision compared to VWF:RCo. Linear regression of VWF:Ab and VWF:RCo across all samples exhibited good agreement (R2= 0.89) with statistical significance (P < 0.001) and bias of -8.7. Concordance was high in classifying samples as normal or abnormal. Analysis of treated samples showed excellent agreement (R2= 0.91) with statistical significance (P < 0.001) and bias of -4.3.
  
  
  CONCLUSIONS
  Our analysis validates the VWF:Ab assay in a prospective study of a large cohort of patient samples and extends these results to post-treatment patient samples.
authors.affiliation: Department of Pathology, New York University School of Medicine, New York, NY, USA.
authors.forename: M
authors.initials: M
authors.lastname: Ettel
authors.affiliation: Department of Pathology, New York University School of Medicine, New York, NY, USA.|Department of Pediatrics, New York University School of Medicine, New York, NY, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Nardi
authors.affiliation: Department of Pathology, New York University School of Medicine, New York, NY, USA.
authors.forename: L
authors.initials: L
authors.lastname: McVoy
mesh_terms: D003894:Deamino Arginine Vasopressin / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D007840:Latex / Q000737:chemistry; D008297:Male; D011446:Prospective Studies; D014842:von Willebrand Diseases / Q000097:blood* / Q000188:drug therapy*; D014841:von Willebrand Factor / Q000008:administration & dosage* / Q000378:metabolism*
chemical_list: D007840:Latex; D014841:von Willebrand Factor; D003894:Deamino Arginine Vasopressin
keywords: Von Willebrand diseases; automation; latex; nephelometry and turbidimetry/methods; von Willebrand factor