In vitro assessment of platelet function

With the realization that the skin bleeding time is often an unreliable measure of platelet function, efforts have been made to identify ways to assess qualitative platelet dysfunction. Currently available techniques measure platelet adhesion, platelet aggregation, the ability of platelets to retard or stop flow through filters, and the contribution of platelets to in vitro clot formation. Glass bead adhesion, which continues to be performed in some laboratories, is gradually being replaced by measures of platelet adhesion to filters composed of glass fibers, Dacron fibers, or collagen. In each instance, anticoagulated platelet-rich plasma or whole blood flows through the filter under a regulated pressure gradient. The amount of blood flowing through the filter versus time and/or the time to filter occlusion are measured. Recent developments in platelet aggregation have focused on whole blood and stagnation point flow aggregation techniques. Whole blood aggregation does not require blood sample processing and accommodates blood obtained from citrated vacutainer tubes. Stagnation point flow measures both platelet adhesion and aggregation and may be able to detect pathologically-enhanced platelet function. Global measures of hemostasis attempt to simultaneously evaluate the adequacy of fluid phase coagulation and platelet function. Currently available techniques include Thromboelastography, SonoClot Analyzer, Hemodyne Hemostasis Analyzer, PITT, and Hemostatometry. Although each of these technologies have been shown to provide interesting data in the research setting, the ability of any of these techniques to detect abnormal or clinical inadequate platelet function remains to be established.