INR Goal for Coumadin in Atrial Fibrillation
For patients with nonvalvular atrial fibrillation on warfarin (Coumadin), the target INR is 2.5 with a therapeutic range of 2.0 to 3.0. 1, 2, 3
Standard Target Range
The ACC/AHA guidelines establish an INR target of 2.0 to 3.0 (target 2.5) for all patients with nonvalvular atrial fibrillation at high risk of stroke receiving warfarin therapy. 1
This target range applies regardless of the pattern of atrial fibrillation—whether paroxysmal, persistent, or permanent—the same INR goal is used. 2
The FDA drug label for warfarin confirms this target INR of 2.5 (range 2.0-3.0) for atrial fibrillation patients based on clinical trial evidence. 3
Atrial flutter should be managed with identical anticoagulation targets as atrial fibrillation. 1, 2
Evidence Supporting This Range
Lower INR targets (below 2.0) significantly increase thromboembolic events without reducing major bleeding risk. A meta-analysis demonstrated that adjusted-dose warfarin (INR 2.0-3.0) reduced thrombosis risk by 50% compared to lower-dose warfarin (INR ≤1.6), with a relative risk of 0.50 (95% CI 0.25-0.97). 4
A 2020 systematic review of 79 randomized trials (n=12,928) found that lower INR targets were associated with 50% higher rates of thromboembolism (7.1% vs 4.4%, RR 1.50) compared to standard targets, despite reducing major bleeding. 5
The 2023 Asian AF trial comparing low-intensity (INR 1.6-2.6) versus standard-intensity (INR 2.0-3.0) anticoagulation showed numerically fewer strokes with standard intensity, though differences were not statistically significant in this underpowered study. 6
Special Populations Requiring Modified Targets
Elderly patients (≥75 years): For those at increased bleeding risk but without absolute contraindications, a lower INR target of 2.0 (range 1.6-2.5) may be considered, though this represents a compromise between efficacy and safety. 2
Mechanical heart valves: If a patient has both atrial fibrillation and a mechanical heart valve, the target INR should be at least 2.5, with specific targets based on valve type and position (often 2.5-3.5 for mitral position or older valve types). 2, 3
Valvular atrial fibrillation (mitral stenosis): Warfarin with standard INR 2.0-3.0 is recommended, as these patients were excluded from NOAC trials. 7
Monitoring Requirements
INR should be measured at least weekly during warfarin initiation. 1, 2
Once anticoagulation is stable, INR monitoring should occur at least monthly. 1, 2
Time in therapeutic range (TTR) should ideally be ≥70% to maximize efficacy and safety; if TTR remains <65% despite interventions, switching to a direct oral anticoagulant should be considered. 2
Common Pitfalls to Avoid
Do not use lower INR targets (1.5-2.0) in an attempt to reduce bleeding risk—this strategy provides only 80% of the stroke prevention efficacy while not significantly reducing major bleeding. 2, 4
Do not assume aspirin is an adequate substitute for warfarin in patients with stroke risk factors—aspirin alone is no longer recommended for stroke prevention in AF regardless of risk level. 2
The evidence supporting lower INR targets comes predominantly from East Asian populations and should not be extrapolated to Western populations without caution. 5