Pokorney SD, Holmes DN, Thomas L, et al. - Because patients with atrial fibrillation (AF) taking warfarin sodium commonly experience bleeding and thrombotic events (eg, stroke and systemic embolism), researchers ascertained if a history of therapeutic warfarin control in patients with AF is independently linked to ensuing bleeding or thrombotic events. Historical international normalized ratio variance was correlated with future bleeding events, but no historical international normalized ratio metrics were related to future stroke risk in this cohort study of 51,830 visits among 10,137 patients with atrial fibrillation. Investigators found that clinical risk scores for major bleeding and thrombotic events were more strongly linked to future clinical events than any international normalized ratio (INR) metrics for warfarin control among patients with AF taking warfarin. Although past INR variability was correlated with future major bleeding events, subsequent thrombotic events were not related to an INR metric. It was difficult to distinguish patients taking warfarin who, despite using multiple metrics of high-quality historical INR control, were at low danger for future major bleeding and thrombotic events.