Monitoring of clopidogrel treatment by multiple electrode platelet aggregometry¹,²

Low responsiveness to clopidogrel is an important cause of adverse events after coronary stenting. Multiple electrode platelet aggregometry (MEA) measured by the Multiplate ® system seems to be suitable for monitoring clopidogrel treatment. We validated this method by analyzing hirudin blood samples from 150 healthy volunteers to establish reference ranges of the MEA tests, from 75 hematologic patients with anemia or thrombopenia to determine the dependence of MEA values on hematocrit (HCT) and platelet count, and from 1005 patients after percutaneous coronary intervention (PCI) and 600 mg clopidogrel loading dose to test the reproducibility of the results under clinical conditions. It was found that MEA results are not affected by the different methods of blood withdrawal and sample transport, if the blood is kept at rest for 30 min before measuring. Measuring must be performed within 3 h after blood withdrawal. It was found that MEA results are not valid in patients with HCT ≤0.30 L/L or platelets ≤100/nL. Because clopidogrel loading also causes a decrease of thrombin receptor-activating peptide (TRAP) values, clopidogrel responsiveness, defined by ADP values under the lower reference level (men: 32 U, women: 46 U), can only reliably be classified if the TRAP value is >20 U and the TRAP/ADP ratio <3. Clopidogrel monitoring should be performed within 24 h after PCI, despite the risk of unclear results in ∼12%. In summary, by concentrating on preanalytical conditions and blood count, MEA is suitable to detect clopidogrel response. The TRAP test should be performed simultaneously to allow a valid assessment.