The international normalized ratio (INR) should be measured monthly once therapeutic levels are achieved and are stable for at least 8 weeks, although treatment should be individualized and an increased frequency may be required by some patients (strength of recommendation [SOR]: C, consensus statements). For highly compliant patients with stable levels and a clear understanding of factors that influence anticoagulation (changes in health, diet, medications), routine monitoring may be extended to 6 weeks (SOR: B, single randomized controlled trial [RCT]) or longer (SOR: C, case series). Patient-managed warfarin therapy, using biweekly self-measurements, results in more time in therapeutic range than routine physicianmanaged care (SOR: A, RCTs)
