title: Variation in platelet function testing has a major influence on detection of aspirin resistance in healthy subjects.
abstract: BACKGROUND
  An increased demand for monitoring aspirin treatment by platelet function tests has been observed, but data on the biological variation of these tests are insufficient. The aim of this study was to assess the biological variation of optical platelet aggregometry and closure time in healthy subjects without aspirin and after aspirin ingestion.
  
  
  METHODS
  In 20 healthy subjects, blood was sampled 4 times: on 2 consecutive mornings a day after aspirin ingestion (100 mg/daily) and on 2 consecutive days of no treatment. In all samples, arachidonic acid-, ADP- and collagen-induced optical platelet aggregation was measured, and closure times were determined by collagen/epinephrine (CEPI) and collagen/ADP (CADP) cartridges in a platelet function analyzer-100.
  
  
  RESULTS
  Aspirin significantly reduced arachidonic acid- and ADP-induced platelet aggregation and significantly prolonged CEPI closure time, but had no significant effect on collagen-induced platelet aggregation and CADP closure time. Aspirin increased both within- and between-subject coefficients of variation. Arachidonic acid-induced platelet aggregation was the most sensitive to aspirin and no aspirin-resistant subjects were detected on either day after aspirin. According to ADP-induced platelet aggregation or CEPI closure time, 25 and 30% of healthy subjects, respectively, changed from aspirin resistant to aspirin responsive or vice versa from one day to another. There was no agreement between platelet function tests in determining aspirin resistance.
  
  
  CONCLUSIONS
  A significant variation in optical platelet aggregometry and closure time exists and is presumed to have a major effect on determination of aspirin resistance.
authors.affiliation: Department of Vascular Diseases, University Medical Centre, Ljubljana, Slovenia. mojca.bozic@kclj.si
authors.forename: Mojca
authors.initials: M
authors.lastname: Bozic-Mijovski
authors.forename: Matej
authors.initials: M
authors.lastname: Rakusa
authors.forename: Mojca
authors.initials: M
authors.lastname: Stegnar
mesh_terms: D000328:Adult; D001241:Aspirin / Q000008:administration & dosage / Q000493:pharmacokinetics*; D001760:Bleeding Time; D003951:Diagnostic Errors; D016903:Drug Monitoring; D004351:Drug Resistance; D005260:Female; D006801:Humans; D008297:Male; D009391:Nephelometry and Turbidimetry; D010974:Platelet Aggregation / Q000187:drug effects*; D010979:Platelet Function Tests / Q000592:standards*; D015203:Reproducibility of Results
chemical_list: D001241:Aspirin