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Availability of non–vitamin K oral anticoagulants has raised the issue of whether patients who receive warfarin anticoagulation and who appear to have stable therapeutic levels are as stable as we think. In this study, researchers examined whether stability of international normalized ratio (INR) values during the first 6 months of anticoagulation predicted future stability. They identified 3749 patients (mean age, 75) with atrial fibrillation who were anticoagulated with warfarin and who had at least three INRs recorded during the first 6 months of anticoagulation and six INRs during the subsequent year. Stability was defined as 80% of readings within the INR therapeutic range (2.0–3.0).
A quarter of patients (968) were considered to be sta…