Aspirin responsiveness in healthy volunteers measured with multiple assay platforms.

Background: We evaluated the sensitivity, precision, and concordance of 4 assays designed to detect aspirin responsiveness or resistance.

Methods: Twenty-nine healthy laboratory volunteers took 80 mg aspirin for 7 days, and a subset of volunteers took 325 mg aspirin for an additional 7 days. We measured platelet function by light transmission aggregometry with arachidonic acid, PFA-100, and VerifyNow. PFA-100 and VerifyNow assays were performed in duplicate to assess method imprecision. Some volunteers had samples taken within 2-4 h of the final dose of aspirin and again within 20-24 h of the final dose. We measured urinary 11-dehydro-thromboxane B(2) at baseline and after 80 or 325 mg aspirin.

Results: No volunteers were nonresponsive to aspirin therapy as measured by the PFA-100. One of 29 participants demonstrated lack of response to aspirin as measured by VerifyNow and urinary 11-dehydro-thromboxane B(2); 2 of 29 demonstrated lack of response as measured by light transmission aggregometry. Imprecision was <10% for the PFA-100 and VerifyNow. Concordance was high (>90%) between all assays. Neither aspirin dose (80 vs 325 mg) nor timing between final dose of aspirin and blood draw (2-4 vs 20-24 h) affected any of the assays.

Conclusions: Light transmission aggregometry, PFA-100, VerifyNow, and urinary 11-dehydro-thromboxane B(2) are all sensitive to the effects of aspirin in healthy individuals. Variables such as aspirin dose, timing between final dose of aspirin and blood collection, and imprecision do not affect the ability of the assays to detect aspirin effect on platelet function.