The INR system of standardizing PT measurements can minimize variability between laboratories, PT reagents, and instruments. The INR system can also facilitate international agreement on therapeutic ranges and allow direct comparison of clinical trials. This should provide greater uniformity in the management of oral anticoagulant therapy and ultimately may improve patient outcomes. ASHP supports the use of the INR system on the basis of studies demonstrating that this system permits warfarin dosing that is less dependent on the variability of thromboplastin reagent sensitivity.