Elevated levels of circulating procoagulant microparticles in patients with paroxysmal nocturnal hemoglobinuria and aplastic anemia

Paroxysmal nocturnal hemoglobinuria (PNH), frequently occurring during supp ressed hematopoiesis including aplastic anemia (AA), is a clonal disorder a ssociated with an increased incidence of thrombotic events. Complement-medi ated hemolysis, impairment of the fibrinolytic system, or platelet activati on are thought to be responsible for the associated thrombotic risk, We inv estigated here the elevation of membrane-derived procoagulant microparticle s in the blood flow of such patients, Elevated levels of circulating microp articles were in fact detected in both de novo PNH patients and AA subjects with a PNH clone, but not in those with AA without a PNH clone. The cellul ar origin of the microparticles was determined in PNH samples; most stemmed from platelets. Glycophorin A(+) particles were rarely detected. Therefore , platelet activation, resulting in the dissemination of procoagulant phosp holipids in the blood flow, could be one of the main causes for the elevate d thrombotic risk associated with PNH. These observations suggest that shed membrane particles can be considered a valuable biological parameter for t he assessment of possible thrombotic complications in patients with PNH. (C ) 1999 by The American Society of Hematology.