INTRODUCTION

As platelets are clearly involved in the pathology of atherosclerosis and arterial thrombosis (Chapters 16 and 17), antiplatelet therapy forms an important component of both treatment and prophylactic strategies (Chapter 21) in high-risk patients with cardiac (Chapter 23), cerebrovascular (Chapter 24), or peripheral vascular disease (Chapter 25). Antiplatelet drugs are also occasionally used as prophylaxis for venous thromboembolism, although anticoagulants are more effective in the venous circulation (Chapter 26). Many types of established and new platelet function tests (Chapter 8) are being investigated to see if they predict those at risk of arterial disease and also for monitoring antiplatelet drugs being given for secondary prevention. In particular, there has been a recent explosion of interest in detecting patients who respond poorly to their antiplatelet therapy, with widespread use of the misleading and poorly defined terms “aspirin resistance” and “clopidogrel resistance.” Although the repertoire of antiplatelet drugs that are now available for clinical use is also likely to increase in the future (Chapter 20), platelet function testing is still not widely used to detect, monitor, or titrate different types of antiplatelet therapy in different patient groups in different clinical settings. The question also remains whether platelet function tests can identify a clinically important “resistance” to aspirin and/or clopidogrel, and if so, how treatment should be modified.