Quantitative determination of circulating platelet microparticles by flow cytometry.

Platelet microparticles are vesicles derived from the plasma membrane of platelets activated by a variety of agonists. To assess the extent of platelet activation, we recently developed a new and simple method of quantitating circulating microparticles in plasma by flow cytometry using the murine monoclonal antibody against glycoprotein IIb-IIIa (NNKY1-32). Using 2-microns fluorescent calibration beads, we succeeded in evaluating the absolute level of circulating microparticles. We determined the microparticle concentrations in 10 patients with arterial occlusive disease and in nine normal healthy donors, to determine whether the detection of microparticles would be useful in assessing the degree of platelet activation in clinical disorders. Microparticle levels were significantly higher in patients not treated with anti-thrombotic drugs than in normal healthy donors (P < 0.001), but not significantly higher in patients with vascular prostheses who had received anti-thrombotic drugs. These observations suggest the usefulness of microparticle quantitation in assessing the platelet activation in arterial occlusive diseases.