Circulating Microparticles and Risk of Venous Thromboembolism.

Abstract 3987 Poster Board III-923 Background Microparticles (MPs) are circulating, submicroscopic fragments ( Aim of the study To investigate the association between high plasma levels of MPs and risk of VTE Patients and Methods In a case-control study, 186 patients with a first episode of VTE (deep venous thrombosis and/or pulmonary embolism) and 418 healthy controls were included. MPs were analyzed by flow cytometry with a gate defined by a 1 μm beads and using APC-Annexin V together with FITC anti-CD41 or FITC anti-CD142 antibodies in order to identify platelet MPs (MP-Plts) and MPs exposing tissue factor (MP-TF), respectively. MPs levels were expressed as number/μL. Results Patients had significantly higher median plasma levels of both MPs-Plts and MPs-TF than controls [1942 vs 1519 (p 95 th percentile of the control group (3633/μL for MPs-Plts and 1113/μL for MPs-TF) than in those with MPs levels ≤95 th percentile [for MPs-Plts: OR=2.59 (95%CI 1.23 – 5.45); for MPs-TF: OR=2.38 (1.15 – 4.92)]. The risk increased in a dose-dependent manner for both MPs-Plts and MPs-TF, particularly above the 75 th percentile of the distribution in controls. The exclusion of patients whose MPs levels were measured within 6 months from VTE (in order to avoid the possible effect of the acute phase on MPs measurements), did not change the results [adjusted OR: 2.63 (1.18 – 5.89) for MPs-Plts and 2.36 (1.10 – 5.19) for MPs-TF]. The Table shows the relative risks of VTE associated with the presence or absence of high MPs levels and thrombophilia. Individuals with MPs >95 th percentile or thrombophilia alone had a 2 to 3-fold increased risk of VTE, whereas those with both MPs-Plts >95 th percentile and thrombophilia had a 9-fold increased risk of VTE. This synergistic effect was confirmed also for MPs-TF and remained after the exclusion of patients whose blood sample was collected within 6 months from VTE [OR 7.72 (1.68-35.4) for MP-Plts and 8.14 (2.08-31.8) for MP-TF]. Conclusions Plasma levels of MPs are significantly higher in patients with VTE than in healthy controls. MPs levels >95 th percentile are associated with a 2.5-fold increased risk of VTE. There is a synergistic interaction between high levels of MPs and thrombophilia on VTE risk. Disclosures: No relevant conflicts of interest to declare.