Comparison of methods to evaluate aspirin-mediated platelet inhibition after percutaneous intervention with stent implantation.

Urinary 11-dehydro thromboxane B2 (d-TXB2) concentrations in the highest quartile have been associated with an increased risk of adverse outcomes in patients at high risk for atherothrombotic events. However, the determination of d-TXB2 is time consuming and not suitable for daily clinical routine. We therefore sought to determine the test correlating best with d-TXB2 to estimate aspirin-mediated platelet inhibition in 225 patients on dual antiplatelet therapy after percutaneous intervention with stent implantation. We selected light transmission aggregometry, the VerifyNow aspirin assay, the Platelet Function Analyzer-100, multiple electrode platelet aggregometry (MEA) and Impact-R for comparisons with d-TXB2. Cut-off values for high on-treatment residual arachidonic acid-inducible platelet reactivity (HRPR) were defined according to quartiles of each assay. Sensitivities and specificities of the different platelet function tests were based on d-TXB2 results. The results from all assays correlated poorly with d-TXB2. Only MEA showed a weak, but significant correlation with d-TXB2 (r = 0.14, p = 0.042). Further, the five platelet function tests showed a poor agreement with d-TXB2 regarding the determination of HRPR. Sensitivities and specificities for HRPR ranged from 17.5 to 44.6%, and from 70.8 to 77.9%, respectively. In conclusion, the evaluated assays did not mirror d-TXB2 results, suggesting that thromboxane inhibition can be circumvented in assays that determine platelet function. Therefore, large trials with clinical outcome data are needed to determine the diagnostic value of the various test systems and to define the gold standard method for assessing residual AA-inducible platelet reactivity.