Predicting Bleeding Risk on Anticoagulant Therapy for Venous Thromboembolism

Oral anticoagulant therapy for patients who are at risk of developing blood clotting
problems is used by between 400,000-600,000 Canadians annually. The use of this drug
represents the most common cause of patient adverse medical outcomes due to medical errors.
Furthermore, many patients have adverse outcomes using these drugs because physicians are
not able to predict which patients are likely to have bleeding outcomes. Much effort has
gone into developing ways to predict which patients are at risk of clotting but almost no
work has gone into ways of predicting which patients would be at high risk of bleeding. This
information is required to balance off the risk-benefits and to enable physicians and
patients to understand the risks and benefits of taking these medications. Our study will
develop a tool that can be used to predict bleeding risk in patients taking oral
anticoagulant therapy. It will enable more informed decision making by both physicians and
patients and will result in better control of the use of these drugs. In addition, patients
who are at risk for being difficult to accurately dose on oral anticoagulants will be
identified through our study.

Inclusion Criteria:

- >=18 years old

- provoked or unprovoked venous thromboembolism

- objectively confirmed venous thromboembolism

- treated with an oral anticoagulant(vitamin K antagonist or new oral anticoagulant)
for at least 3 months with plans to continue long-term

- if taking a vitamin K antagonist; INR target is between 2.0-3.0

- if taking a vitamin K antagonist; must have taken it for the last 3 consecutive weeks
(minimum)

Exclusion Criteria:

- major bleeding while taking oral anticoagulants

- active bleeding at study enrollment

- active cancer - current or at the time of VTE diagnosis

- unable to provide written informed consent

- refusal to provide written informed consent