title: Comparison of Von Willebrand factor (VWF) activity VWF:Ac with VWF ristocetin cofactor activity VWF:RCo.
abstract: BACKGROUND
  Ristocetin cofactor activity of Von Willebrand factor (VWF:RCo) and the ratio VWF:RCo to its antigen VWF:Ag are used as routine screening to estimate VWF function and to detect types of Von Willebrand disease (VWD) caused by loss of high molecular weight multimers. However, the VWF:RCo test is prone to analytic imprecisions due to various reasons. We compared an assay for VWF activity (VWF:Ac) with VWF:RCo putting emphasis on the ratios to VWF:Ag.
  
  
  METHODS
  We evaluated 942 samples from 432 patients and evaluated three groups in detail: normal patients (normal multimers, VWF:Ag and VWF:RCo >0.5 U/ml, VWD type 1 excluded; n=258), VWD type 1 (n=76) and acquired Von Willebrand syndrome (AVWS, n=326). In addition, 30 healthy subjects were analysed.
  
  
  RESULTS
  VWF:Ac and VWF:RCo correlated well (Pearson´s r=0.96, p<0.01), so did their ratios to VWF:Ag (Pearson´s r=0.82, p<0.01). We calculated the normal range of VWF:Ac/VWF:Ag for healthy subjects as 0.8-1.16. In comparison, the reference range (mean±2std) derived from normal patient samples was 0.73-1.14. The corresponding ranges for VWF:RCo/VWF:Ag came to 0.74-1.23 (healthy) and 0.62-1.25 (normal patients). The ratios showed similar results regarding VWD type 1. The sensitivity for AVWS was higher with VWF:Ac/VWF:Ag than with VWF:RCo/VWF:Ag (97.5% versus 84.7%).
  
  
  CONCLUSIONS
  The data suggest that the results obtained with the VWF:Ac assay are comparable to that of the VWF:RCo assay. An AVWS was more reliably detected by VWF:Ac/VWF:Ag. We assume that the VWF:Ac assay could replace VWF:RCo for routine screening for AVWS, especially when prompt evaluation is required.
authors.affiliation: Institute of Clinical Chemistry and Laboratory Medicine, Freiburg, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Geisen
authors.affiliation: Laboratory for Hemostaseology, Department of Pediatrics and Adolescent Medicine, Freiburg, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Zieger
authors.affiliation: Laboratory for Hemostaseology, Department of Pediatrics and Adolescent Medicine, Freiburg, Germany.
authors.forename: Lea
authors.initials: L
authors.lastname: Nakamura
authors.affiliation: Dept. of Hematology and Oncology, University Freiburg Medical Center, Freiburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Weis
authors.affiliation: Dept. of Hematology and Oncology, University Freiburg Medical Center, Freiburg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Heinz
authors.affiliation: Goodheart Institute & Foundation Rotterdam, European Bloodcoagulation Science Center, Rotterdam, The Netherlands.
authors.forename: Jan Jacques
authors.initials: JJ
authors.lastname: Michiels
authors.affiliation: Department of Cardiovascular Surgery, Heart Center University of Freiburg, Freiburg, Germany. Electronic address: claudia.heilmann@universitaets-herzzentrum.de.
authors.forename: Claudia
authors.initials: C
authors.lastname: Heilmann
mesh_terms: D000328:Adult; D000941:Antigens / Q000378:metabolism*; D005260:Female; D006403:Hematologic Tests / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012310:Ristocetin / Q000378:metabolism*; D012680:Sensitivity and Specificity; D014842:von Willebrand Diseases / Q000097:blood / Q000175:diagnosis / Q000378:metabolism*; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D000941:Antigens; D014841:von Willebrand Factor; D012310:Ristocetin
keywords: Acquired Von Willebrand syndrome; Ristocetin cofactor activity of Von Willebrand factor; Von Willebrand disease; Von Willebrand factor activity