Venous thromboembolism (VTE), including pulmonary embolism (PE) and deep vein thrombosis (DVT), is a major health problem all over the world [1]. VTE has a long-term risk of recurrence, and the prevention of recurrent VTE by anticoagulation therapy is essential for the long-term management of patients with VTE [2]. International Society on Thrombosis and Haemostasis (ISTH) recommends classifications of risk of recurrent VTE based on whether an episode of VTE is unprovoked or provoked by an environmental risk factor and, if it is provoked, whether the provoking risk factor is transient or persistent [3].
