Use of an extended INR follow-up interval for Veteran patients in an anticoagulation clinic

A prospective, single-arm study of 50 participants evaluated an extended INR follow-up interval to determine the implementation feasibility and safety of an extended interval in Veterans on a stable dose of warfarin. A protocol was designed to allow for a rigorous, yet pragmatic evaluation of a 12-week INR follow-up interval. Feasibility was determined by study enrollment, retention, and participant achievement rates for the extended INR interval. Safety was determined by bleeding and thromboembolism rates. Participants were monitored for 6 months. Despite the long-term stability of participants prior to enrollment, only 56% achieved a 12-week follow-up interval and only 34% of enrolled participants maintained a 12-week interval. Sixteen percent of participants were never eligible for an extension of their INR follow-up interval despite meeting initial enrollment criteria. There were two major bleeding events and one participant who experienced a thromboembolic event. Implementation of an extended interval of INR follow-up appears feasible as participant enrollment goals were met and pharmacists were able to follow the study protocol. However, a lower than expected proportion of participants were able to achieve and maintain an extended INR follow-up interval. Future evaluations are needed to confirm the safety of an extended INR interval.