Value of platelet activation markers as prothrombotic risk indicators

Platelets adhere to the subendothelium that is exposed at sites of vessel wall injury to form a primary haemostatic plug by aggregating together. Activated platelets support fibrin formation by exposing a procoagulant surface and encrypting circulating tissue factor. Through this process platelets are essential components of haemostasis and also of arterial thrombosis. Evidence has been provided that detection of circulating activated and/or hyperreactive platelets may indicate a high thrombotic risk. The aim of the present review is to present an overview of the various parameters that can be measured and that provide information on platelet activation and reactivity, such as changes in platelet surface membrane properties (e.g. CD62P expression, binding of PAC-1, fibrinogen or annexin V), release of stored compounds (e.g. beta-thromboglobulin, platelet factor 4 or CD62P), formation of procoagulant membranous microvesicles, measurements of platelet adhesion, platelet aggregation and platelet-leukocyte conjugate formation and changes in platelet volume. The methods that can be used to measure the various parameters are briefly described. We also refer to various pitfalls in pre-analysis and data interpretation. Throughout we direct the readers' attention to published studies that indicate the potential value of the various measured parameters as indicators of thrombotic risk.