Venous thromboembolism (VTE) including deep vein thrombosis (DVT) and pulmonary embolism (PE) affects about 1,200,000 individuals each year in Europe. About 50% of VTE are unprovoked and 20% of these patients will face a recurrent event after the usual three to six-month course of anticoagulant treatment. To date, most patients are given prolonged anticoagulant treatment. However, anticoagulant treatment are associated with a major risk of bleeding (3%/year). Thus an accurate identification of patients with unprovoked VTE with a low risk of recurrence is needed to avoid unnecessary anticoagulant treatment with a risk of bleeding.

Over the past few years, microparticles (MPs) which are small vesicles originating from the budding of cellular membranes have emerged as important biological entities regulating hemostasis. MPs expose at their surface procoagulant molecules such as phosphatidylserin and tissue factor (TF). All data obtained in mouse models support a role of MPs in venous thrombosis mediated by the TF activation. Moreover, results from clinical studies showed that TF-MPs was associated with the risk of venous thrombosis. However, the predictive value of TF-MPs in the recurrence of VTE is unknown. Besides, no study has taken into account the recent progresses in the understanding of the role of MPs in haemostasis. Indeed, MPs vectorize molecules which are not only procoagulant but also profibrinolytic. The net result depends on a balance between both activities (the coagulo-lytic balance). This balance is can be measured by two complimentary assays on MPs.

We hypothesized that the coagu-lytic balance of MPs is associated with an increased risk of VTE recurrence after stopping the anticoagulant treatment.

Inclusion Criteria:

• adult patients with a VTE history with at least 3 months of anticoagulant treatment.

Exclusion Criteria:

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300 adult patients with a VTE history with at least 3 months of anticoagulant treatment. 150 patients which suffered from a re-thrombosis within 5 years after stopping the anticoagulant treatment, will be age- and sex-matched with 150 without thrombosis recurrence.