Patients opting for combination antiplatelet therapy rather than treatment with an oral anticoagulant should be informed that they are choosing an inferior treatment with regard to stroke prevention. Recommendation 2.1.10. For patients with AF, including those with paroxysmal AF, who are at high risk of e558S Antithrombotic Therapy for Atrial Fibrillation bleeding risk because there are insuf cient data to estimate reliably the absolute bleeding rates for patients in different categories of bleeding risk on different antithrombotic regimens. However, the following evidence regarding bleeding risk assess- ment may help to guide individualized treatment decisions for patients with AF. One challenge in bleeding risk assessment for patients with AF is that many of the factors associ- ated with an increased risk of major bleeding are also risk factors for ischemic stroke. For instance, older age, hypertension, congestive heart failure, and prior history of ischemic stroke all of which are compo- nents of the CHADS2 score have been found in various studies of patients with AF to be indepen- dent predictors of bleeding while on VKA therapy.94 Several bleeding risk scores have been evaluated in cohorts of patients with AF (see Table 11).53,95-98 However, these scores have not been extensively validated. Their ability to predict major bleeding is modest, with comparable C statistics across exter- nal validation studies (range, 0.61-0.66).53,97-99 In sce- narios where we make weak recommendations in favor of oral anticoagulation (eg, patients with a CHADS2 score of 1), patients at high risk of major bleeding may decline oral anticoagulation. Additional Risk Factors for Stroke in Patients With AF In addition to consideration of bleeding risk and patient values and preferences, for patients with a CHADS2 score of 0 or 1, clinicians may wish to consider additional stroke risk factors when indi- vidualizing decisions about antithrombotic therapy. 