Feasibility of Extended-interval Follow-up for Patients Receiving Warfarin

AimsThe 2012 American College of Chest Physician Evidence-Based Management of Anticoagulant Therapy guidelines suggest an international normalized ratio (INR) testing interval of up to 12weeks, rather than every 4weeks, for patients with consistently stable INRs while taking vitamin K antagonists. We aimed to examine the feasibility of extended-interval follow-up in a real-world setting. MethodsPatients receiving stable warfarin therapy for 12weeks at baseline began extended-interval follow-up with visits occurring at 6weeks, 14weeks, and every 12weeks thereafter to a maximum of 68weeks or until they were no longer suitable for extended-interval follow-up. A single INR excursion >0.3 from goal was permitted if a reversible precipitating factor was identified and the INR was expected to return to goal without dose adjustment. The primary outcome was the proportion of patients completing all study follow-up visits. ResultsOf 48 patients enrolled, 47 had evaluable data. The most common indication for anticoagulation was atrial fibrillation/flutter (53.2%). At baseline, mean prior warfarin treatment duration was 6.76years and median number of weeks on a stable regimen was 24weeks (IQR, 19-37.5). Eleven patients (23%) completed all study follow-up visits, whereas 17 (36%) did not maintain a stable INR past the 14-week follow-up. ConclusionA large proportion of patients with previously stable (3months) INRs were not able to maintain stable INRs during extended-interval follow-up. More research is needed to identify patient characteristics predictive of success with extended-interval follow-up prior to broad implementation.