G.D. Barnes, X. Kong, D. Cole, B. Haymart, E. Kline‐Rogers, S. Almany, M. Dahu, M. Ekola, S. Kaatz, J. Kozlowski, J.B. Froehlich

A prior single center randomized trial suggested that patients with stable INR values could safely receive INR testing as infrequently as every 12 weeks. To test the implementation success of an extended INR testing interval for stable warfarin patients in a practice-based, multi-center collaborative of anticoagulation clinics. At six anticoagulation clinics, patients were identified as being eligible for extended INR testing based on prior INR value stability and minimal warfarin dose changes between 2014 and 2016. We assessed the frequency with which anticoagulation clinic providers recommended an extended INR testing interval (>5 weeks) to eligible patients. We also explored safety outcomes for eligible patients, including next INR values, bleeding events, and emergency department visits. At least one eligible period for extended INR testing was identified in 890/3362 (26.5%) warfarin-treated patients. Overall, the use of extended INR testing in eligible patients increased from 41.8% in 2014/Q1 to 69.3% in 2016/Q4. The number of subsequent out-of-range next INR values were similar between eligible patients who did and did not receive an extended INR testing interval (27.3% vs. 28.4%, respectively). The number of major bleeding events were not different between the two groups, but rates of clinically relevant non-major bleeding (0.02/100-patient-years vs. 0.09/100-patient-years) and emergency department visits (0.07/100-patient-years vs. 0.19/100-patient-years) were lower for eligible patients with extended vs. non-extended INR testing intervals. Extended INR testing for stable warfarin patients can be successfully and safely implemented in diverse, practice-based anticoagulation clinic settings. This article is protected by copyright. All rights reserved.