The invention provides methods of determining risk for stroke in a patient, as well as methods of determining a subject's need for anti-coagulation therapy. In exemplary embodiments, the method comprises measuring a level of derivatives of reactive oxygen metabolites (DROMs) in a biological sample obtained from the subject, wherein an increased level of DROMs, relative to a control level, is indicative of the subject's need for anticoagulation therapy. Further provided are methods of decreasing risk of stroke in a subject, methods of determining the efficacy of a therapeutic agent, methods of monitoring a subject's risk of stroke, and kits.