Traditional model of platelet aggregation. (A) Based on studies with the platelet aggregometer, 3 key elements have been identified as important for platelet aggregation: an activating stimulus (typically a soluble agonist), a plasma protein (predominantly fibrinogen), and a platelet surface receptor (integrin αIIbβ3 or GPIIb-IIIa). Agonist-induced activation of integrin αIIbβ3 is essential for the binding of fluid-phase fibrinogen, which as a consequence of its dimeric structure, can physically bridge 2 adjacent platelets. (B) The platelet aggregometer is a relatively simple technique that involves stirring a suspension of platelets in the presence of a platelet activating substance and by monitoring changes in light transmission, the device can accurately monitor platelet clumping (aggregation) in suspension.
