title: Validation of an automated latex particle-enhanced immunoturbidimetric von Willebrand factor activity assay.
abstract: BACKGROUND
  Laboratory diagnosis of von Willebrand disease (VWD) requires accurate measurement of plasma von Willebrand factor (VWF) activity.
  
  
  OBJECTIVE
  To evaluate laboratory characteristics, diagnostic accuracy and testing utilities of an automated latex particle-enhanced immunoturbidimetric VWF assay (VWF:Lx) based on a monoclonal antibody recognizing the VWF-platelet glycoprotein (GP) Ib binding domain.
  
  
  METHODS
  Laboratory characteristics including lower detection limit, linearity, precision, sample stability, and method comparison between VWF:Lx and VWF ristocetin cofactor activity by platelet aggregometry (VWF:RCo) were examined. To assess VWF:Lx diagnostic accuracy, 492 patient plasma samples, including 40 previously characterized VWD patient samples, were tested for VWF antigen (VWF:Ag) and VWF:RCo by either aggregometry or flow cytometry, and VWF:Lx with supplemental VWF multimer analysis when indicated. Based on results of VWF:Ag, VWF:RCo and VWF multimer analysis, and available clinical information, samples were categorized as: normal; VWD types 1, 2A/B, 2M, or severe 1 vs. 2M; or acquired VWF abnormalities (AVWA) due to subtle loss of highest molecular weight multimers.
  
  
  RESULTS
  VWF:Lx had excellent laboratory characteristics and linear correlation with VWF:RCo (R(2) = 0.93). VWF:Lx accurately classified virtually all normal and VWD patient samples. Compared with VWF:RCo, VWF:Lx had superior sensitivity and specificity for distinguishing severe type 1 vs. 2M VWD and identifying AVWA. A proposed screening panel comprising VWF:Ag and VWF:Lx had 100% and 83% sensitivity for detecting VWD and AVWA, respectively.
  
  
  CONCLUSIONS
  VWF:Lx has excellent laboratory characteristics and diagnostic accuracy compared with VWF:RCo, and can be used as part of an initial VWD screening panel and as a supplementary test.
authors.affiliation: Special Coagulation Laboratory, Division of Hematopathology, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN 55905, USA. chen.dong@mayo.edu
authors.forename: D
authors.initials: D
authors.lastname: Chen
authors.forename: J I
authors.initials: JI
authors.lastname: Tange
authors.forename: B J
authors.initials: BJ
authors.lastname: Meyers
authors.forename: R K
authors.initials: RK
authors.lastname: Pruthi
authors.forename: W L
authors.initials: WL
authors.lastname: Nichols
authors.forename: J A
authors.initials: JA
authors.lastname: Heit
mesh_terms: D001331:Automation; D005434:Flow Cytometry; D006801:Humans; D007840:Latex; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D014842:von Willebrand Diseases / Q000097:blood / Q000175:diagnosis*; D014841:von Willebrand Factor / Q000032:analysis*
chemical_list: D007840:Latex; D014841:von Willebrand Factor