INR Goal for Atrial Fibrillation
The target INR for patients with atrial fibrillation on warfarin is 2.0 to 3.0, with an optimal target of 2.5. 1, 2, 3, 4, 5
Standard Target Range
All major guidelines consistently recommend an INR range of 2.0 to 3.0 for nonvalvular atrial fibrillation, regardless of whether the AF pattern is paroxysmal, persistent, or permanent. 1, 5, 6
The optimal target to aim for within this range is an INR of 2.5, as this maximizes the proportion of time spent in the therapeutic range and provides the best balance between stroke prevention and bleeding risk. 2, 3, 4
This same INR target of 2.0 to 3.0 applies equally to atrial flutter. 1, 6
Evidence Supporting This Range
Multiple randomized controlled trials demonstrate that INR 2.0 to 3.0 provides maximum protection against ischemic stroke while minimizing bleeding complications. 1, 3
Lower INR targets (such as 1.6 to 2.5 or 1.5 to 2.0) provide only approximately 80% of the stroke protection achieved with standard-intensity anticoagulation. 1, 3, 4
A meta-analysis of randomized controlled trials showed that adjusted-dose warfarin (INR 2.0-3.0) compared with lower dose warfarin (INR ≤1.6) significantly reduced the risk of any thrombosis (RR 0.50,95% CI 0.25-0.97) without statistically increasing major hemorrhage risk. 7
A 2020 systematic review of 79 RCTs (n=12,928) found that lower INR targets were associated with higher rates of thromboembolism (7.1% vs 4.4%, RR 1.50) compared to standard targets, despite lower bleeding rates. 8
Regional Variations Should Be Avoided
Some Asian countries have proposed using a lower target INR range (1.6-2.6), especially in elderly patients. 4, 8
However, current guidelines explicitly state there is no robust evidence for implementing a target INR range of 1.6 to 2.6, and therefore the conventional, evidence-based INR target of 2.0 to 3.0 should be employed globally. 3, 4, 8
Special Populations
Age alone (including patients >75 years) is not a contraindication to standard-intensity anticoagulation with INR 2.0-3.0. 1, 6
Patients with mechanical heart valves require higher INR targets: for tilting disk or bileaflet valves in the mitral position, the target INR is 3.0 (range 2.5-3.5). 1, 5, 6
Patients with severe chronic kidney disease or on dialysis should still target an INR of 2.0-3.0 when warfarin is used for atrial fibrillation. 2
Remote myocardial infarction does not alter the target INR for atrial fibrillation anticoagulation; the target remains 2.0-3.0. 2
Monitoring Requirements
INR should be checked at least weekly during warfarin initiation until stable therapeutic levels are achieved. 1, 2, 5
Once stable in therapeutic range, INR monitoring should occur at least monthly. 1, 2, 5
The goal is to maintain time in therapeutic range (TTR) ≥65-75%, as TTR below this threshold is independently associated with increased risk of adverse events. 2, 4
Common Pitfalls
An INR above 3.5 is associated with significantly increased bleeding risk, particularly intracranial hemorrhage. 2
Random "one-off" INR values provide little insight into anticoagulation quality; focus should be on the average TTR over time. 4
In newly initiated warfarin patients with AF, approximately 25% fail to reach INR stabilization (defined as three consecutive INR values between 2.0-3.0), and even after initial stabilization, 30% of subsequent INR values remain out of range. 9
More frequent monitoring may be required during initiation of warfarin therapy or when other drugs that interact with warfarin are started or stopped. 1