Long-Term Aspirin and Clopidogrel Response Evaluated by Light Transmission Aggregometry, VerifyNow, and Thrombelastography in Patients Undergoing Percutaneous Coronary Intervention

BACKGROUND: A reduced response to aspirin and clopidogrel predicts ischemic events, but reliable tests are needed to identify low responders. We compared 3 platelet-function tests during long-term dual treatment with aspirin and clopidogrel. METHODS: Patients who underwent a percutaneous coronary intervention and were receiving a combination of 325 mg/day aspirin and 75 mg/day clopidogrel were followed for 1 year. Blood was sampled 5 times during this period for 3 tests: light transmission aggregometry (LTA) assay, with 5.0 mu mol/L ADP or 1.0 mmol/L arachidonic acid (AA) used as an agonist; VerifyNow (TM) assay, with the P2Y(12) or aspirin cartridge (Accumetrics); and thrombelastography (TEG), stimulated by 2.0 mu mol/L ADP or 1.0 mmol/L AA. RESULTS: Twenty-six of 33 patients completed all scheduled visits. A low response to clopidogrel was found in a few patients at variable frequencies and at different visits, depending on the method and criteria used. We found a moderate correlation between the LTA (ADP) and VerifyNow (P2Y(12) cartridge) results, but the TEG (ADP) results correlated poorly with the LTA and VerifyNow results. A low response to aspirin was found with the VerifyNow (aspirin cartridge) and TEG (AA) methods on 6 and 2 occasions, respectively, but not with the LTA (AA) method, except for 1 occasion caused by probable noncompliance. CONCLUSIONS: Detecting a low response to clopidogrel depends largely on the method used. Which method best predicts ischemic events remains uncertain. A low response to aspirin is rare with AA-dependent methods used at the chosen cutoffs. In some patients, the response to clopidogrel or aspirin may be classified differently at different times, even with the same method. (C) 2010 American Association for Clinical Chemistry