title: Monitoring aspirin therapy with the Platelet Function Analyzer-100.
abstract: OBJECTIVE
  Low platelet response to aspirin has been reported to be associated with a high incidence of vascular events. The reported prevalence of aspirin low-responsiveness varies, which may be explained by poor reproducibility of the methods used to evaluate aspirin response and low compliance. The Platelet Function Analyzer-100 (PFA-100) is a commonly used platelet function test. We aimed to assess the reproducibility of the PFA-100 and the agreement with optical platelet aggregometry (OPA) in healthy volunteers and in patients with coronary artery disease (CAD) treated with low-dose aspirin.
  
  
  METHODS
  Twenty-one healthy volunteers and 43 patients with CAD took part in the study. During treatment with aspirin 75 mg daily, all participants had platelet function assessed in duplicate with the PFA-100 and OPA on 4 consecutive days. Additionally, platelet function was assessed before aspirin treatment in healthy subjects. Serum-thromboxane B(2) (S-TxB(2)) was measured to assess compliance.
  
  
  RESULTS
  In healthy volunteers not receiving aspirin, duplicate measurements resulted in coefficients of variation (CV) of 7.9 % for the PFA-100 and 5.2 % for OPA. During aspirin treatment, CVs were significantly higher (healthy volunteers: PFA-100: 15.6 %, OPA: 19.2 %; patients: PFA-100: 26.6 %, OPA: 16.8 %). Two of the 64 participants were classified as aspirin low-responders with both methods, indicating poor agreement (Kappa coefficient 0.05). Compliance was excellent, as S-TxB(2) was completely inhibited in all participants.
  
  
  CONCLUSIONS
  Aspirin treatment affects the reproducibility of both PFA-100 and OPA. This imprecision should be considered carefully if the methods are used for monitoring aspirin treatment. Additionally, these methods do not identify the same individuals as being aspirin low-responders.
authors.affiliation: Department of Cardiology, Aarhus University Hospital Skejby, Aarhus, Denmark.
authors.forename: Jette
authors.initials: J
authors.lastname: Mortensen
authors.forename: Tina Svenstrup
authors.initials: TS
authors.lastname: Poulsen
authors.forename: Erik Lerkevang
authors.initials: EL
authors.lastname: Grove
authors.forename: Jens
authors.initials: J
authors.lastname: Refsgaard
authors.forename: Helle Ladefoged
authors.initials: HL
authors.lastname: Nielsen
authors.forename: Susanne Bendesgaard
authors.initials: SB
authors.lastname: Pedersen
authors.forename: Sofie Sommer
authors.initials: SS
authors.lastname: Thygesen
authors.forename: Anne-Mette
authors.initials: AM
authors.lastname: Hvas
authors.forename: Steen Dalby
authors.initials: SD
authors.lastname: Kristensen
mesh_terms: D000328:Adult; D016718:Arachidonic Acid / Q000494:pharmacology; D001241:Aspirin / Q000627:therapeutic use*; D003324:Coronary Artery Disease / Q000188:drug therapy; D005260:Female; D006262:Health; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D010974:Platelet Aggregation / Q000187:drug effects; D010979:Platelet Function Tests / Q000295:instrumentation*
chemical_list: D016718:Arachidonic Acid; D001241:Aspirin