Appropriate international normalized ratio follow-up interval for patients with atrial fibrillation taking warfarin

Abstract

Background: The recommended follow-up for international normalized ratio (INR) measurement is every 4 weeks in patients with atrial fibrillation (AF) who take warfarin. However, data regarding the appropriate INR follow-up interval are lacking in these patients.

Objective: We aimed to investigate the appropriate INR follow-up intervals in patients with AF receiving warfarin between 6- and 12-week intervals for follow-up appointments.

Methods: We retrospectively enrolled patients with AF taking warfarin at the Central Chest Institute of Thailand between January 2017 and May 2023. The primary outcome was the time in therapeutic range (TTR) for each follow-up interval group, and the secondary outcome was the composite outcome of acute ischemic stroke/transient ischemic attack (TIA)/systemic embolic events, major bleeding, minor bleeding, and/or allcause mortality between the 6- and 12-week groups.

Results: A total of 400 patients with AF taking warfarin were recruited for the study. The average CHA2DS2- VASc score was 3.6 and 3.7 in the 6- and 12-week groups, respectively. The average HAS-BLED score was 1.8 in both groups. The TTR in the 12-week group was not inferior to that in the 6-week group (absolute difference 1.5 percentage points; 95% confidence interval –2.4 to 5.3; P < 0.001 for non-inferiority). In addition, the incidence of acute ischemic stroke/TIA/systemic embolic events, major bleeding, minor bleeding, and/or all-cause mortality was not significant between patients in the 6- and 12-week groups.

Conclusion: The TTR in the 12-week group was not inferior to that in the 6-week group in patients with AF taking warfarin. Thus, an extended 12-week follow-up interval may be applied in clinical practice. A larger prospective study will be required in the future.