Comparison of four laboratory methods to assess aspirin sensitivity.

The purpose of this study was to compare the ability of four commercial platelet function assays to detect aspirin response in normal individuals taking 81 or 325 mg aspirin in a single-dose response and then in a 7-day dosing regimen. We employed the Chronolog 570VS whole-blood aggregometer with agonists 1.0 microgram/ml collagen and 0.5 mmol/l arachidonic acid, the PFA-100 epinephrine/collagen cartridge closure time, the Accumetrics Verify/Now arachidonic acid cartridge, and the urine 11-dehydrothromboxane immunoassay normalized to urine creatinine. Fifty normal individuals who met the inclusion criteria were consented in the single-dose study. Blood and urine were collected at baseline, and then each participant was given a 81 mg enteric-coated aspirin tablet. Blood and urine were collected after 24 h. After a minimum of 14 days the process was repeated with a 325 mg aspirin dose. Forty-five individuals were enrolled in the 7-day study. Blood and urine were collected at baseline. Then each participant was given an 81 mg dose of aspirin daily for 7 days. After 7 days, blood and urine specimens were obtained and tested. After a minimum washout period of 14 days the process was repeated using a 7-day regimen of 325 mg enteric-coated aspirin tablet. Student's t-test indicated statistical significance between baseline and post responses in both dosing regimens (P < 0.05). Individuals were not consistently identified as aspirin responsive across all platforms. All assays discriminated between platelet response and nonresponse to aspirin at both dosages. It may be necessary to employ multiple assays to detect individual platelet response.