National Assessment of Warfarin Anticoagulation Therapy for Stroke Prevention in Atrial Fibrillation

Abstract

Background— Anticoagulation control with warfarin, as assessed by the international normalized ratio (INR), is challenging. Time in the therapeutic range has been inversely correlated with major hemorrhage, thrombosis, and mortality. Quest Diagnostics offers standardized INR laboratory testing services to approximately half of US physician practices. To inform national stroke prevention strategies, we evaluated anticoagulation control in office-based community practices. Methods and Results— We selected individuals with ≥2 months of INR data, INR results of >1.2, and an ICD-9 diagnosis code of atrial fibrillation. Frequency of INR testing and time in the therapeutic range were analyzed by age, sex, length of testing period, number of referred patients per provider, and median household income (based on home ZIP code). We identified 138 319 individuals referred by 37 939 physicians, yielding a total of 2 683 674 INR results. Patients had a mean age of 74 years; 81% were ≥65 years of age, and 55% were ≥75 years of age. The mean time in the therapeutic range was 53.7% overall and improved with time on treatment, increasing from 47.6% for patients with <6 months of testing to 57.5% for those with ≥6 months of testing ( P <0.0001). The number of patients tested per physician practice was positively associated with time in the therapeutic range. Younger age, female sex, and lower income were also independently associated with poorer anticoagulant control. Conclusion— This study demonstrates widespread suboptimal anticoagulation control, suggesting an urgent need to improve oral anticoagulation care for most patient segments in the United States.