[Methods of studying platelet function. Biological markers of the activation of human platelets in vivo and in vitro].

Platelets play a key role in hemostasis, thrombosis, atherosclerosis and their pathological consequences. It is possible to follow platelet activation in vivo by measuring bleeding time, platelet count, existence of circulating platelet aggregates or platelet survival and sequestration. In vitro tests include measurement of platelet adhesion, aggregation alpha, and dense granule secretion. It is also possible to follow biochemical events linked to platelet activation such as prostaglandin metabolism, Ca2+ levels or platelet membrane modifications (receptors, glycoproteins, coagulant activities, antigens). Some of these markers of platelet activation are modified in diseases (thrombotic events, hyperlipoproteinemia) and the use of artificial surfaces. It is not always possible to know if the modifications are the cause or the consequence of the pathological event. Unfortunately, some results are questionable because of methodological procedures. Some of these tests have been used to follow the involvement of platelets in a pathological event or to evaluate a prethrombotic state in a patient. It is not yet possible to identify directly, or by the mean of a marker of platelet activation, a patient who is likely to experience a thrombotic episode.