9. Laboratory tests for vWD

  • Bleeding time
    • Lack of sensitivity and specificity
  • Factor VIII
    • may or may not be decreased
  • PT, PTT
    • PTT may be prolonged, but normal PTT does not rule out vWD
    • PT normal
  • von Willebrand factor antigen
    • ELISA or LIA test
      • monoclonal antibody for epitope on vWF molecule
  • Ristocetin cofactor activity - functional assay for vWF
  • Multimer analysis
  • Ristocetin cofactor activity
    • antibiotic which induces vWF binding to GP1b on platelets
    • normal lyophilized platelets are mixed with patient plasma and ristocetin
    • platelet agglutination measured (no secondary wave)
    • HMWM most important in absence of platelet activation
      Ristocetin Cofactor Assay