Outpatient self-management of warfarin therapy: a pilot study

Self-testing and adjusting of warfarin dosages by patients is an evolving strategy for management of oral anticoagulation. We performed this open, prospective, 3-month pilot study to assess the feasibility of conducting a large, randomized trial comparing self-managed with physician-managed anticoagulation. Ten competent patients with planned anticoagulation for at least 3 months were provided education on warfarin therapy and trained to use an individualized warfarin nomogram. International normalized ratios (INRs) were determined weekly for 12 weeks and reported with warfarin dosages to the investigator for the first 8 weeks only. Eight patients elected to use a home monitor (ProTime) to measure INRs. Patients maintained 76.5% (range 50-91.7%) of INRs within the target range. In 119 dosage adjustment decisions, there were only 3 errors (2.5%). No bleeding or thrombotic complications occurred. To confirm concordance, initial and final INRs were measured concurrently by the ProTime monitor and laboratory. The mean absolute difference for 16 paired INR determinations was 0.33 (range 0.02-0.9). All patients expressed satisfaction and a desire to continue with self-management. This pilot study provides support for conducting a prospective, large-scale, randomized trial.