Novel Strategies for Assessing Platelet Reactivity

Abstract

There are many approaches to assessing platelet reactivity and many uses for such measurements. Initially, measurements were based on the ability of platelets separated from other blood cells to aggregate together following activation with an appropriate 'aggregating agent'. Later, measurements of platelet aggregation in blood itself were performed, and this led to a point-of-care approach to platelet function testing. Measurement of secretory activity through the appearance of the activation marker Pselectin on platelets now provides an alternative approach, which enables remote testing. Measurement of vasodilator-stimulated phosphoprotein phosphorylation is also moving toward application in situations remote from the testing laboratory. Here we provide an overview of the various approaches that are now available, assess their advantages and disadvantages, and describe some of the clinical situations in which they are being used. Keywordsaspirin, flow cytometry, light transmission aggregometry (LTA), multiplate electrode aggregometry (MEA), P-selectin, P2Y12 antagonists, platelet aggregation, platelet reactivity, VASP phosphorylation, VerifyNow Platelet reactivity is a broad term indicating the degree of the response of blood platelets to an external stimulus, usually an 'aggregating agent'. Platelet reactivity can be measured in many different ways and the purpose of this review is to summarize the approaches, with an emphasis on the newer approaches that are becoming available.Platelets play an important role in the hemostatic process [1,2]. They contribute to the formation of a hemostatic plug that serves to prevent blood loss from injured blood vessels. The hemostatic plug contains thousands of platelets that have aggregated together within a network of fibrin. However, platelets also contribute to the generation of a thrombotic mass in a coronary or cerebral artery or in an artificial stent leading to blockage and resulting in conditions such as heart attack, stroke and stent thrombosis [3,4]. A thrombus is also composed of platelet aggregates within a fibrin network. So thrombus formation can thus be considered to be hemostasis in the wrong place.

A Remote Assay for Measuring Canine Platelet Activation and the Inhibitory Effects of Antiplatelet Agents

“…In addition to inherent problems in studying platelet physiology, equipment to test platelet function is expensive and requires a high level of technical expertise to operate. Similar problems are encountered with remote analysis of human platelets …”

“…Consequently, once fully validated, it might be possible for this method to help optimize treatment with either aspirin or clopidogrel in animals. Once refined, the availability of a simple to use test for remote analysis of platelet activity will enable a better understanding of the relationship between the effectiveness of drugs acting as inhibitors of platelet function and clinical outcome; in the same way as has been established in humans …”

“…Similar problems are encountered with remote analysis of human platelets. [21][22][23] Preliminary studies using the fixative paraformaldehyde, for analyzing canine platelet activity, suggested this could have clinical utility for delayed analysis. 24 A method for remotely testing platelet activity has recently been developed for humans, based on the use of PAM-Fix a (Platelet Solutions Ltd, Nottingham, UK).…”

Measurement of platelet p-selectin expression by flow cytometry in patients with acute ischemic stroke

“…Flow cytometry is an advantageous technique for the analysis of platelet receptors (30). Measurement of secretory activity through the appearance of the activation marker p-selectin on platelets now provides an alternative approach, which enables remote testing (31). Flow cytometry offers several advantages over other clinical tests of platelet function including relative simplicity, minimal manipulation of samples, preventing artifactual in vitro platelet activation, analysis in the physiological milieu of whole blood, high sensitivity for the detection of platelet subpopulations and the need for only minimal blood volumes.…”

Management of Hemostasis for Pediatric Patients on Ventricular-Assist Devices

“…23 Also, there is limited correlation between assay methods. [24][25][26] Platelet aggregometry is considered to be the gold standard for platelet function assays. According to a recent international survey, 93% laboratories use platelet-rich plasma (PRP), and 7% laboratories use whole blood.…”