von Willebrand disease

- most common inherited bleeding disorder
- VWF serves two roles
  i) major adhesion molecule that tethers the platelet to exposed subendothelium
  ii) binding protein for FVIII
- males and females are equally affected but disease manifestation is more obvious in female due to menstruation and associated menorrhagia
- screening test are PT, APTT, factor VIII activity, vWF activity and vWF antigen level determination
- ristocetin is an antibiotic that causes vWF to bind to and activate platelet causing platelet agglutination. Degree of platelet agglutination is proportional to concentration of plasma vWF