OBJECTIVETo establish a flow cytometric internal standard method for counting platelet-derived microparticles (PMPs) and to study its clinical significance.

METHODSPMPs suspension (platelet poor plasma, PPP) was extracted by gradual centrifugation. According to the size of PMPs, 3 microm and 0.8 microm latex beads were used as internal standards for the quantitation. PMPs were counted by adjusting flow cytometric discrimination and voltage of forward scatter and side scatter.

RESULTSIn 30 healthy donors, the average concentration of resting PMPs was (1.2 x 10(5) +/- 5.7 x 10(4))/ml and that of activated PMPs was (1.6 x 10(6) +/- 9.1 x 10(5))/ml. Compared with healthy donors, PMPs mean value was significantly higher (P < 0.001) in 18 patients with coronary artery disease, 12 with acute cerebral infraction and 23 with chronic renal failure [the average PMPs concentration, (6.1 x 10(5) +/- 2.5 x 10(5))/ml, (6.8 x 10(5) +/- 3.4 x 10(5))/ml and (5.9 x 10(5) +/- 3.1 x 10(5))/ml respectively]. However, no significant difference in PMPs concentration was observed in 25 patients with acute leukemia and severe thrombocytopenia during the aplastic phase after chemotherapy [(1.3 x 10(5) +/- 6.1 x 10(4))/ml, (P > 0.05)].

CONCLUSIONSPMPs is a useful indicator in monitoring platelet activation, and plays an important role in thrombotic disease. By flow cytometric internal standard method, PMPs can be counted rapidly and accurately, which may be very helpful in interlaboratory comparative studies.