Microparticles are small membrane fragments with dimension between 0.1 and 1 μm, which are released during cell activation or apoptosis, exposing the phospholipid phosphatidylserine and membrane antigens typical for cellular origin. Philadelphia-negative myeloproliferative neoplasms (MPNs) are characterized by an increased risk of thrombosis. Data from literature suggest an association between thrombosis and the procoagulant activity of microparticles. Association between the procoagulant activity of microparticles and the incidence of thrombosis was assesed in a group of 126 patients with Philadelphia-negative MPNs. Measurement of microparticles procoagulant activity was performed using a functional assay, namely the Zymuphen MP-activity (Hyphen Biomed, Neuville-sur-oise, France). A total of 539 samples were analysed within this group of patients, regardless of patients' state of health. A significantly higher circulating microparticles procoagulant activity was found in MPN patients as compared with the control group (P < 0.001). A pathological level of procoagulant activity was observed more frequently in patients with polycythaemia vera (88%, P = 0.002) than groups of patients with essential thrombocythaemia (73.2%) and primary myelofibrosis (68.3%); the same result was confirmed in patients with a history of venous thrombosis in comparison with patients without thrombosis (84.7 vs. 73.2%, P = 0.029). Patients without cytoreductive treatment had a higher activity of microparticles (P = 0.010). Furthermore, presence of JAK2 V617F mutation was associated with an increased procoagulant activity (P = 0.007), as well as the higher JAK2 V617F allele burden (P = 0.001). Further prospective clinical studies will be necessary to evaluate the clinical relevance of microparticles in the prediction hypercoagulable state in these patients.

Department of Haematology University Hospital Brno bMedical Faculty cInstitute of Biostatistics and Analyses Masaryk University Brno Brno Czech Republic

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