Platelet factor 3 in plasma fractions: Its relation to microparticle size and thromboses

Platelet factor 3 (PF3) was assayed by Russell's viper venom (RVV) in three plasma fractions, platelet-rich plasma (PRP), platelet poor plasma (PPP), and 0.1 μm particlefiltered plasma (PFP), in 42 healthy controls, 34 patients with recent cerebrovascular accidents (CVA) and 28 with recent ischemic events from coronary artery disease (CAD). Platelet microparticles (PMP) were assayed in PPP by flow cytometry. Relative to controls, the RVV clotting times were shortened in all three plasma fractions in both patient groups, p<0.001. PMP were also elevated in both patient groups, p<0.001. Linear regression analysis showed that the RVV times of PPP are inversely correlated with PMP, p<0.005, in patient groups but not in controls. There was no correlation of RVV time with PT, APTT or FIB. After converting RVV times to units of PF3 activity, it could be shown that only about 1/4 of the total PF3 activity was contributed by platelets. The major contribution to the PF3 activity in controls was from microparticles <0.1 μm but in patients was due mainly to microparticles >0.1 μm. The RVV time was superior to routine coagulation tests in discriminating thrombotic patients from healthy controls.