Take Home Message: In cardiovascular medicine there are several circumstances when it is valuable to give anticoagulant medications (blood thinners). These medicines reduce the chance of clot formation and lower the risk of strokes and heart attacks. Because it is harder to form clots patient will have a higher risk of bleeding. In atrial fibrillation, we have good criteria for evaluating the risk of clotting and stroke (CHADS2 and CHADS-VASC) but are in search of a good score to help doctors and patients predict bleeding risk when on the blood thinner coumadin (warfarin). The HAS-BLED score http://www.mdcalc.com/has-bled-score-for-major-bleeding-risk/ performed best, but not very well in this analysis except for its ability to predict the most serious type of bleeding called intracranial hemmorhage.