Background: Frequent home monitoring of the International Normalized Ratio (INR) has been proposed as an alternative to office monitoring in patients requiring warfarin (Coumadin) for anticoagulation. Several studies have reported a possible link between weekly self-testing and improved patient outcomes. In addition to involving patients in their own care, self-testing may also allow for a more rapid response to INR values outside the therapeutic range. Several handheld fingerstick devices have been approved for home use. Matchar and colleagues conducted the Home INR Study to determine whether self-testing of INR is more effective than office testing at reducing the risk of a major event (i.e., stroke, major bleeding episode, or death).
The Study: Patients were eligible to participate if they were able to reliably perform self-testing, and if they required long-term warfarin therapy for atrial fibrillation, a mechanical heart valve, or both. Participants were randomized to receive INR testing in an office setting or to perform self-testing at home. Office testing was performed monthly at anticoagulation clinics that used standardized procedures for anticoagulation management. Home-based self-testing was performed weekly with an approved device, and patients reported the results to study staff for dosing instructions. The primary end point was the time to a first major event. Secondary end points included time within the INR target range, patient satisfaction, and quality of life.
Results: A total of 2,922 patients were followed for a mean of three years (range = 2 to 4.75 years). Of these, 2,236 had atrial fibrillation without a mechanical heart valve, 684 had a mechanical valve, with or without atrial fibrillation, and two had neither a mechanical valve nor fibrillation. Adherence rates for scheduled INR testing were higher in the self-testing group (87 percent versus 52 percent in the office-testing group. Discontinuation rates were similar between groups. No significant differences were observed between groups regarding the risk of developing a major event or in the time to developing a major event. Patients in the self-testing group remained within the therapeutic INR range for a greater percentage of time than those in the office-testing group (absolute difference = 3.8 percentage points; P < .001). The self-testing group also had greater patient satisfaction with anticoagulation therapy. More patients in the self-testing group reported minor bleeding episodes than those in the office-testing group (22 versus 17 percent; P < .01).
Conclusion: Compared with past studies in which home testing showed a reduction in major adverse events, this study showed that weekly self-testing of INR was nearly equivalent to monthly office testing in the risk of death, major bleeding episode, or stroke, as well as the time to the first episode of one of these events. Self-testing was associated with modest improvements in time within the therapeutic INR range and in patient satisfaction with anticoagulation therapy. The authors conclude that self-testing should be considered for patients whose access to high-quality anticoagulation care is limited.