What is the target international normalized ratio (INR) for patients with deep vein thrombosis (DVT) on warfarin therapy?

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. 1

Therapeutic Range and Target

• The therapeutic INR range of 2.0 to 3.0 (target 2.5) is strongly recommended over lower ranges (INR <2.0) or higher ranges (INR 3.0-5.0) for all treatment durations in DVT patients 1
• This recommendation is based on moderate-certainty evidence and represents a strong recommendation from the CHEST guidelines 1
• The American Society of Hematology (ASH) provides a strong recommendation for this INR range over lower ranges such as 1.5 to 1.9 1

Evidence Supporting This Range

Lower INR ranges are inferior and potentially dangerous:

• Using an INR range lower than 2.0 to 3.0 significantly increases the risk of recurrent DVT (relative risk 3.25, with 24 more DVT events per 1000 patients) 1
• Low-intensity warfarin (INR 1.5-1.9) results in 2.8 times higher risk of recurrent venous thromboembolism compared to conventional-intensity (INR 2.0-3.0) 2
• 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 1
• Importantly, low-intensity warfarin does NOT reduce bleeding risk compared to conventional-intensity therapy 2

Maintaining therapeutic INR improves outcomes:

• Patients who maintain INR values between 2.0 and 3.0 have significantly higher rates of complete DVT resolution (68% complete resolution rate) 3
• Median INR values were significantly higher in patients achieving complete DVT resolution compared to those with incomplete resolution 3
• Patients with subtherapeutic INR values had higher rates of incomplete DVT resolution and subsequent chronic venous insufficiency 3

Initiation and Bridging Requirements

• Warfarin should be started early (same day as parenteral anticoagulation) and overlapped with parenteral therapy (LMWH, fondaparinux, or UFH) for a minimum of 5 days AND until INR is ≥2.0 for at least 24 hours 1, 4, 5
• This bridging period is critical because warfarin initially creates a prothrombotic state before achieving therapeutic anticoagulation 5
• If INR falls below therapeutic range during treatment, restart bridging with LMWH until INR returns to 2.0-3.0 for at least 24 hours 4

Common Pitfalls to Avoid

Do not use lower INR targets thinking they are safer:

• Historical INR targets below 2.0 (such as 1.7 or 1.8) originated from conversion errors when different thromboplastin reagents were used and have never been validated for safety or efficacy 1
• These subtherapeutic targets persist in clinical practice without objective evidence and should be avoided 1

Do not discontinue parenteral anticoagulation prematurely:

• Failing to bridge with LMWH when INR is subtherapeutic is a critical error that increases recurrent thrombosis risk 4
• The overlap must continue for the full 5 days minimum, even if INR reaches 2.0 earlier 1, 5

Monitor consistently:

• Patients with INR values frequently below therapeutic range have worse outcomes including incomplete thrombus resolution and higher rates of post-thrombotic syndrome 3
• Consider medication interactions, dietary vitamin K intake, and adherence issues if INR is difficult to maintain in range 4, 5

Special Considerations

• 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 5
• Higher INR ranges (3.0-4.5) are NOT recommended for DVT and increase bleeding risk without additional benefit 1
• The target INR of 2.0-3.0 applies regardless of whether the DVT is provoked or unprovoked, though duration of therapy differs 4, 5