Under what circumstances would you consider anticoagulation in a young female patient with persistently elevated factor XI activity?

While this is a known risk factor for venous [Meijers et al NEJM 2000] and potentially arterial [Yang et al, Am J Clin Pathol 2006] thrombosis, it is unclear to what extent this should affect the decision for anticoagulation. Would this affect your decision for anticoagulation in a patient with prior venous thrombosis with transient risk factors? With history of stroke/CVA? During pregnancy/postpartum?