title: Prevalence of persistent platelet reactivity despite use of aspirin: a systematic review.
abstract: BACKGROUND
  The absolute risk of recurrences among patients using aspirin for prevention of cardiovascular events remains high. Persistent platelet reactivity despite aspirin therapy might explain this in part. Reported prevalences of this so-called aspirin resistance vary widely, between 0% and 57%.
  
  
  OBJECTIVE
  The aim of the study was to systematically review all available evidence on prevalence of aspirin resistance and to study determinants of reported prevalence.
  
  
  METHODS
  Using a predefined search strategy, we searched electronic databases MEDLINE, EMBASE, CENTRAL, and Web of Science. To be included in our analysis, articles had to contain a laboratory definition of aspirin resistance, use aspirin as secondary prevention, and report associated prevalence.
  
  
  RESULTS
  We included 34 full-text articles and 8 meeting abstracts. The mean prevalence of aspirin resistance was 24% (95% CI 20%-28%). After adjustment for differences in definition, used dosage, and population, a statistically significant higher prevalence was found in studies with aspirin dosage < or =100 mg compared with > or =300 mg (36% [95% CI 28%-43%] vs 19% [95% CI 11%-26%], P < .0001). Studies measuring platelet aggregation using light aggregometry with arachidonic acid as an agonist had a pooled unadjusted prevalence of 6% (95% CI 0%-12%). In studies using point-of-care platelet function-analyzing devices, the unadjusted prevalence was significantly higher, at 26% (95% CI 21%-31%).
  
  
  CONCLUSIONS
  Prevalences widely differ between studies reporting on aspirin resistance. Both aspirin dosage and the method of defining aspirin resistance strongly influence estimated prevalence, which explains found heterogeneity among studies. On average, it appears that about 1 in 4 individuals may express biochemically defined aspirin resistance.
authors.affiliation: Department of General Internal Medicine and Endocrinology, Leiden University Medical Center, Leiden, The Netherlands. m.m.c.hovens@lumc.nl
authors.forename: Marcel M C
authors.initials: MM
authors.lastname: Hovens
authors.forename: Jaapjan D
authors.initials: JD
authors.lastname: Snoep
authors.forename: Jeroen C J
authors.initials: JC
authors.lastname: Eikenboom
authors.forename: Johanna G
authors.initials: JG
authors.lastname: van der Bom
authors.forename: Bart J A
authors.initials: BJ
authors.lastname: Mertens
authors.forename: Menno V
authors.initials: MV
authors.lastname: Huisman
mesh_terms: D001241:Aspirin / Q000627:therapeutic use*; D004351:Drug Resistance; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use*; D015995:Prevalence
chemical_list: D010975:Platelet Aggregation Inhibitors; D001241:Aspirin