Ever since the introduction of warfarin into routine clinical practice, maintenance of a therapeutic INR in patients has proven to be a difficult task, with patients only spending an average of 57-66% of the time within therapeutic range. As the majority of these patients in Canada are treated by primary care providers, busy family physicians must keep a watchful eye on INR values, which are constantly changing due to diets with varying amounts of Vitamin K, not to mention the effects of interacting drugs and other confounders.