Platelet activation and its role in thrombin generation in platelet-induced thrombin generation time

Platelet-induced thrombin generation time (PITT) is a newly developed globa l coagulation assay in which a small amount of partially anticoagulated pla telet-rich plasma (PRP) is rotated in a disc-shaped cuvette within the ligh t beam of a photometer. The time intervals from onset of rotation until agg regation and coagulation of the sample are registered. The aim of our study was to compare platelet activation with generation of thrombin during rota tion of PRP in PITT system. Aliquots of PRP were taken before, 1, 3, and 8 min after the onset of rotation as well as at the beginning of aggregation and shortly before coagulation. Thrombin activity was measured with chromog enic substrate S-2238. We have also measured the level of generated prothro mbin activation fragment 1 + 2 (F1 + 2), which reflects the concentration o f liberated thrombin. Platelet activation was assayed by means of platelet factor 4 (PF4) and beta -thromboglobulin (beta -TG) concentration and regis tration of the aggregation. The concentrations of the Fl + 2, PF4, beta -TG increased very slowly from the beginning of the test until aggregation occ urred. From the start of aggregation, the levels of F1 + 2 rose rapidly. In contrast to the F1 + 2 measurements, thrombin activity has not been detect ed from onset of rotation until the end of the test. Only trace thrombin ac tivity was detectable just after the plasma sample had been clotted in the cuvette. Our results demonstrate that there exists a close relationship bet ween platelet activation and thrombin generation. Viable platelets, which a dhered to the cuvette walls, form an active template on which thrombin can be generated from prothrombin. (C) 2000 Elsevier Science Ltd. All rights re served.