title: Screening for aspirin responsiveness after transient ischemic attack and stroke: comparison of 2 point-of-care platelet function tests with optical aggregometry.
abstract: OBJECTIVE
  Recent studies suggest that patients who do not respond to aspirin (ASA) therapy may be at increased risk of ischemic vascular events. The availability of simple to use point-of-care (POC) platelet function tests now potentially allows aspirin nonresponsiveness to be identified in routine clinical practice. However, there are very few data on whether the different tests produce consistent results. We therefore compared 2 POC tests (PFA-100 device and the Ultegra-RPFA [RPFA]) with conventional light transmission aggregometry (LTA).
  
  
  METHODS
  Platelet function was assessed by all 3 tests in 100 patients receiving low-dose ASA therapy after transient ischemic attack (TIA) or ischemic stroke.
  
  
  RESULTS
  The incidence of ASA nonresponsiveness was 17% by the RPFA and 22% by the PFA-100, compared with only 5% by LTA (ie, as defined with both arachidonic acid and ADP). Agreement between the RPFA and the PFA-100 and arachidonic acid induced LTA was poor (kappa=0.16, 95% CI, -0.08 to 0.39, P=0.11; and kappa=0.09 -0.12 to 0.30, P=0.32, respectively). Agreement between the 2 POC tests was also poor (kappa=0.14, -0.08 to 0.36, P=0.15). Only 2% of patients were aspirin nonresponders by all 3 tests.
  
  
  CONCLUSIONS
  The prevalence of apparent ASA nonresponsiveness was higher with both the POC tests than with LTA. However, agreement between the tests was poor and very few patients were ASA nonresponsive by all 3 tests. Aspirin nonresponsiveness is therefore highly test-specific and large prospective studies will be required to determine the prognostic value of each of the separate tests.
authors.affiliation: Oxford Haemophilia Centre & Thrombosis Unit, Churchill Hospital, Oxford, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Harrison
authors.forename: Helen
authors.initials: H
authors.lastname: Segal
authors.forename: Kevin
authors.initials: K
authors.lastname: Blasbery
authors.forename: Charlene
authors.initials: C
authors.lastname: Furtado
authors.forename: Louise
authors.initials: L
authors.lastname: Silver
authors.forename: Peter M
authors.initials: PM
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D000368:Aged; D001241:Aspirin / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D002546:Ischemic Attack, Transient / Q000175:diagnosis / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D010974:Platelet Aggregation; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use*; D010979:Platelet Function Tests; D019095:Point-of-Care Systems; D011379:Prognosis; D020521:Stroke / Q000175:diagnosis / Q000188:drug therapy*; D017211:Treatment Failure
chemical_list: D010975:Platelet Aggregation Inhibitors; D001241:Aspirin