title: Fainting induces an acute increase in the concentration of plasma factor VIII and von Willebrand factor.
abstract: OBJECTIVE
  von Willebrand factor (VWF) is stored in the Weibel-Palade bodies of endothelial cells and may be released in response to different secretion stimuli such as stress, physical exercise, adrenaline, DDAVP and thrombin.
  
  
  METHODS
  We found that fainting can also induce an acute increase in plasma VWF and factor FVIII (FVIII) concentrations, following observations in two patients with von Willebrand's disease (VWD) who experienced a fainting episode during venipuncture for blood collection.
  
  
  RESULTS
  One patient was classified as having type Vicenza VWD, the other as type 1 VWD; both had normal platelet VWF content. After the fainting episode, FVIII and VWF levels were significantly higher than the levels in blood samples collected without stress; mean increases were 4.35-fold for FVIII, 4-fold for VWF:Ag and 5.3-fold for VWF:RCo, with values overshooting the upper limit of the normal range. Moreover, the post-fainting plasma VWF multimer pattern was characterized by a significant increase in all oligomers with the appearance of unusually large VWF multimers, similar to those observed following DDAVP infusion.
  
  
  CONCLUSIONS
  These findings demonstrate that fainting acts as a stimulus capable of inducing the release of VWF from endothelial cells, and further highlight the role of stress in determining hemostatic states potentially favorable to the development of thrombotic complications.
authors.affiliation: Department of Medical and Surgical Sciences, Padova, Italy. sandra.casonato@unipd.it
authors.forename: Alessandra
authors.initials: A
authors.lastname: Casonato
authors.forename: Elena
authors.initials: E
authors.lastname: Pontara
authors.forename: Antonella
authors.initials: A
authors.lastname: Bertomoro
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Cattini
authors.forename: Carmen
authors.initials: C
authors.lastname: Soldera
authors.forename: Antonio
authors.initials: A
authors.lastname: Girolami
mesh_terms: D000328:Adult; D005169:Factor VIII / Q000032:analysis*; D005260:Female; D006403:Hematologic Tests; D006801:Humans; D018962:Phlebotomy / Q000009:adverse effects; D013575:Syncope / Q000097:blood* / Q000209:etiology; D014842:von Willebrand Diseases / Q000150:complications; D014841:von Willebrand Factor / Q000032:analysis*
chemical_list: D014841:von Willebrand Factor; D005169:Factor VIII