 Genotyping patients at the onset of warfarin anticoagulation may allow more precise dosing. This may translate into fewer major bleeding and clotting events as well as fewer out-of-target-range INRs, which serve as a surrogate for bleeding and clotting complications. During the first several weeks following prescription of warfarin, INR laboratory tests are obtained frequently, often twice weekly. Better predictive assessment of the optimal dose will decrease laboratory costs and improve convenience for patients. 