title: A new definition of aspirin non-responsiveness by platelet function analyzer-100 and its predictors.
abstract: BACKGROUND
  Aspirin non-responsiveness has been described as having a normal closure time (CT) by platelet function analyzer (PFA)-100 assay despite confirmed treatment with aspirin. There is no standard definition of aspirin non-responsiveness by PFA-100, with a variety of cut-off values having been used. We proposed an alternative definition of aspirin non-responsiveness by PFA-100 assay.
  
  
  METHODS
  One hundred eighty-four patients with diagnosis of stable coronary artery disease or diabetes mellitus were included in the study. Blood samples were drawn before and after the 7 days of aspirin therapy. An individual was labelled as aspirin non-responder if his/her post-aspirin CT was not 2SD above his/her baseline CT, where SD was calculated from the baseline CTs of the study population. Aspirin non-responsiveness was also defined as having a normal post-aspirin CT (< or =193 s) regardless of pre-aspirin CT.
  
  
  RESULTS
  The baseline CT ranged 82-187 s (mean 129.1 +/- 27.5, median 128 s) in the study population. At the end of 1 week of aspirin administration, CT increased to a mean of 260.7 +/- 63.6 s (range 102-301). According to our definition, 28 (15.2%) of 184 patients were aspirin non-responders. Univariate analysis indicated that aspirin non-responsiveness was closely associated with gender (P = 0.012) diabetes (P = 0.006), smoking (P = 0.0496) and hypertension (P = 0.021). Multivariate analysis identified diabetes (P = 0.016) as the only significant independent predictor for the presence of aspirin non-responsiveness. Thirty-four of 184 patients (18.5%) classified as aspirin non-responders according to the second criteria. Seven patients with prolongation of post-aspirin CT more than 2SD were classified as aspirin non-responders by the second criteria. Only 1 patient without prolongation of CT more than 2SD was classified as aspirin responsive by the second criteria.
  
  
  CONCLUSIONS
  Definition of aspirin non-responsiveness as post-aspirin CTs < or =193 s might overestimate the prevalence of aspirin non-responsiveness. Nevertheless, definition of aspirin non-responsiveness by PFA-100 must be standardized and its utility as a predictor of cardiovascular events needs to be further investigated.
authors.affiliation: Department of Cardiology, Gazi University School of Medicine, Ankara, Turkey. abaci@gazi.edu.tr
authors.forename: Adnan
authors.initials: A
authors.lastname: Abaci
authors.forename: Mustafa
authors.initials: M
authors.lastname: Caliskan
authors.forename: Fahri
authors.initials: F
authors.lastname: Bayram
authors.forename: Yucel
authors.initials: Y
authors.lastname: Yilmaz
authors.forename: Mustafa
authors.initials: M
authors.lastname: Cetin
authors.forename: Ali
authors.initials: A
authors.lastname: Unal
authors.forename: Servet
authors.initials: S
authors.lastname: Cetin
mesh_terms: D001241:Aspirin / Q000008:administration & dosage / Q000627:therapeutic use*; D003324:Coronary Artery Disease / Q000097:blood / Q000175:diagnosis / Q000188:drug therapy*; D003920:Diabetes Mellitus / Q000097:blood / Q000175:diagnosis / Q000188:drug therapy*; D004032:Diet; D004351:Drug Resistance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage / Q000627:therapeutic use*; D010979:Platelet Function Tests / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity
chemical_list: D010975:Platelet Aggregation Inhibitors; D001241:Aspirin