Target INR for DVT on Warfarin Therapy
For patients with deep vein thrombosis (DVT) treated with warfarin, the target INR is 2.5 with a therapeutic range of 2.0 to 3.0 for all treatment durations. 1, 2, 3
Therapeutic Range and Strength of Recommendation
The American College of Chest Physicians (ACCP) recommends maintaining an INR range of 2.0 to 3.0 with a target of 2.5 for DVT treatment, based on Grade 1B evidence (strong recommendation, moderate certainty). 1
The American Society of Hematology (ASH) provides a strong recommendation for using an INR range of 2.0 to 3.0 over lower ranges (such as 1.5-1.9) for patients who have completed primary treatment and continue VKA therapy as secondary prevention. 1
The FDA-approved warfarin labeling specifies that the dose should be adjusted to maintain a target INR of 2.5 (INR range 2.0 to 3.0) for all treatment durations of venous thromboembolism. 3
Evidence Against Lower INR Targets
Using an INR range lower than 2.0 to 3.0 significantly increases the risk of recurrent DVT, with a relative risk of 3.25 and 24 additional DVT events per 1000 patients. 2
A randomized controlled trial directly comparing low-intensity warfarin (INR 1.5-1.9) versus conventional-intensity warfarin (INR 2.0-3.0) demonstrated that low-intensity therapy resulted in 2.8 times higher risk of recurrent venous thromboembolism (1.9 vs 0.7 per 100 person-years) without reducing bleeding risk. 4
Lower INR ranges may increase the risk of pulmonary embolism (relative risk 5.0) and mortality (relative risk 2.0), though these did not reach statistical significance. 2
Critical Initiation Requirements
Warfarin must be overlapped with parenteral anticoagulation (LMWH or UFH) for a minimum of 5 days AND until the INR is ≥2.0 for at least 24 hours. 2, 5, 3
Warfarin should be started on the same day as parenteral anticoagulation, not after it. 2
This bridging period is essential because warfarin initially creates a prothrombotic state before achieving therapeutic anticoagulation. 2
Common Pitfalls to Avoid
Historical INR targets below 2.0 (such as 1.7 or 1.8) are not validated for safety or efficacy and must be avoided. 2
Failing to bridge with LMWH when INR is subtherapeutic increases recurrent thrombosis risk substantially. 2, 6
Premature discontinuation of parenteral anticoagulation before both the 5-day minimum AND INR ≥2.0 for 24 hours criteria are met. 5, 3
Special Populations
For cancer-associated DVT, LMWH monotherapy is preferred over warfarin when possible, but if warfarin is used, the same INR target of 2.0-3.0 applies. 1, 2, 5
Cancer patients have particular difficulty maintaining therapeutic INR (only 46% of time in therapeutic range in one large trial) due to drug interactions with chemotherapy, anorexia, emesis, and frequent procedure interruptions. 1
Higher INR ranges (such as 3.0-4.5 or 3.0-5.0) are not recommended for DVT and increase bleeding risk without additional benefit. 2