This Figure depicts the odds ratios for risk of thromboembolic events and risks of intracranial hemorrhage vs serum INR levels.[74] The clinical target for anticoagulation therapy is an INR target between 2 and 3, the point where physicians want to keep most of their patients with AFib. The risk of stroke increases below an INR of 1.8, and the risk of intracranial hemorrhage starts to increase at an INR above the 3.1 to 3.5 range. Thus, as evident in the Figure, the range of maximum benefit and minimum risk is a warfarin INR level between 1.8-1.9 and 3.1-3.5; this means maintaining an INR between 2 and 3 will be safe and effective, but that is a very narrow therapeutic window.

Rothman SA. Am J Med 2013; 126: 00-00.