Platelet Function Testing in Patients on Antiplatelet Medications

Guidelines provide a Class IA recommendation for the use of dual antiplatelet therapy in patients undergoing percutaneous coronary intervention (PCI). However, there is interindividual variability in the pharmacodynamic response to antiplatelet medications. Some patients present with a status of high on-treatment platelet reactivity (HPR) during platelet function testing after standard doses of antiplatelet drugs, reflecting a failure to achieve adequate platelet inhibition. As an example, patients with HPR on clopidogrel are at increased risk for thrombotic events, particularly for stent thrombosis and myocardial infarction, but cardiovascular mortality is also elevated. On the contrary, low on-treatment platelet reactivity or an enhanced response to antiplatelet medications has been linked to a higher risk for bleeding. Although both thrombotic and bleeding events are multifactorial in origin, there is supportive evidence for the prognostic value of platelet function testing for risk prediction of both sides of the coin. However, although small studies have provided evidence that treatment adjustments based on platelet function testing results may improve clinical outcomes, the available randomized controlled trials showed no benefit of modifying antiplatelet treatment based on platelet function testing. This review presents the current evidence regarding platelet function testing in patients undergoing PCI. The prognostic value of platelet function testing regarding ischemic and bleeding events is highlighted. Furthermore, the value of platelet function testing for guiding treatment and possible explanations for the so-far negative trial results are presented. The possible future role of platelet function testing for individualized antiplatelet treatment regimens in high-risk patients will be also discussed.