title: Correlation between von Willebrand factor antigen, von Willebrand factor ristocetin cofactor activity and factor VIII activity in plasma.
abstract: BACKGROUND
  The laboratory diagnosis of von Willebrand Factor (VWF) deficiencies includes qualitative and quantitative measurements of VWF and clotting factor VIII (FVIII). Since the FVIII activity is frequently normal in patients with mild type 1 or 2 von Willebrand disease (VWD), there is controversy whether FVIII testing should accompany VWF Antigen (VWF:Ag) assay.
  
  
  METHODS
  The aim of this study was to explore the correlation between VWF:Ag, VWF ristocetin cofactor activity (VWF:RCo) and FVIII in 213 consecutive patients undergoing screening for VWD.
  
  
  RESULTS
  Forty-six patients were identified with VWF:Ag levels lower than the diagnostic threshold (54 IU/dl). A significant correlation was observed between VWF:Ag and VWF:RCo (r = 0.892; p < 0.001), VWF:Ag and FVIII (r = 0.834; p < 0.001), VWF:RCo and FVIII (r = 0.758; p < 0.001). Receiver operating characteristic curve analysis of the VWF:Ag assay revealed an area under the curve of 0.978 and 0.957 for detecting life-threatening values of FVIII (<30 IU/dl) and VWF:RCo (<40 IU/dl), respectively. The negative and positive predictive values at the VWF:Ag threshold value of 54 IU/dl were 100% and 33% for detecting life-threatening FVIII deficiencies, 94% and 80% for identifying abnormal values of VWF:RCo.
  
  
  CONCLUSIONS
  Due to the excellent correlation between VWF:Ag and FVIII and to the diagnostic efficiency of VWF:Ag for identifying abnormal FVIII levels in patients with VWF deficiency, routine measurement of FVIII may not be necessary in the initial screening of patients with suspected VWD. However, the limited negative predictive value of VWF:Ag for identifying type 2 VWD does not allow to eliminate VWF:RCo or VWF:FVIIIB assays from the diagnostic workout.
authors.affiliation: Sezione di Chimica Clinica, Dipartimento di Scienze Morfologico-Biomediche, Università di Verona, Ospedale Policlinico G.B. Rossi, Piazzale Scuro, 10, Verona, 37134, Italy. ulippi@tin.it
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lippi
authors.forename: Massimo
authors.initials: M
authors.lastname: Franchini
authors.forename: Gian Luca
authors.initials: GL
authors.lastname: Salvagno
authors.forename: Martina
authors.initials: M
authors.lastname: Montagnana
authors.forename: Giovanni
authors.initials: G
authors.lastname: Poli
authors.forename: Gian Cesare
authors.initials: GC
authors.lastname: Guidi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D002648:Child; D005169:Factor VIII / Q000032:analysis*; D006801:Humans; D008875:Middle Aged; D011237:Predictive Value of Tests; D012372:ROC Curve; D055815:Young Adult; D014842:von Willebrand Diseases / Q000097:blood / Q000175:diagnosis*; D014841:von Willebrand Factor / Q000032:analysis*