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

Study Questions:

What is the quality of anticoagulation control for patients treated with warfarin from stroke prevention in atrial fibrillation (SPAF) in community-based practices across the United States?


A registry of 138,319 patients, treated for at least 2 months with warfarin for SPAF and who had international normalized ratio (INR) lab tests performed by Quest Diagnostics, was analyzed to explore control on warfarin therapy in the general US population. Quality of warfarin control was measured using the Rosendaal’s time in the therapeutic range (TTR).


Population-wide TTR was 53.7%, increasing with extended time on treatment. Mean TTR was 47.6% for patients with <6 months of warfarin therapy compared to 57.5% for patients with ≥6 months of warfarin therapy (p < 0.0001). Nearly 95% of providers had fewer than 10 patients receiving INR testing. In the multivariate regression analysis, independent predictors of higher TTR included increasing age, male gender, increasing physician case load, and increasing median income.


The authors concluded that this study demonstrates widespread suboptimal anticoagulation control and suggested that focused efforts be made to improve the quality of anticoagulation control across the United States.


Using a unique nationwide database of INR testing services for about half of all US physicians, this study highlights the important difference in the quality of anticoagulation control between the ‘real world’ and the numerous randomized trials. The reported quality of warfarin therapy is similar to other ‘real world’ US populations, but noticeably lower than those achieved in some European countries. Additionally, it highlights the challenges in achieving high-quality anticoagulation care outside of large-volume anticoagulation management centers. When reviewing the randomized trials comparing the new target-specific oral anticoagulants to warfarin, practitioners must now question how well those findings translate into their individual clinical practice.

Clinical Topics: Anticoagulation Management

Keywords: Stroke, Warfarin, Regression Analysis, United States

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