Target INR for DVT on Warfarin Therapy
The goal INR for patients with DVT on warfarin is 2.5, with a therapeutic range of 2.0 to 3.0, maintained throughout the entire treatment duration. 1, 2, 3
Therapeutic Range and Target
The American College of Chest Physicians establishes a target INR of 2.5 with a therapeutic range of 2.0 to 3.0 for all patients with DVT treated with vitamin K antagonists, regardless of treatment duration. 1
This recommendation is supported by the American Heart Association and American College of Cardiology, who both endorse the same 2.5 target with 2.0-3.0 range for DVT and pulmonary embolism. 3
The American Society of Hematology provides a strong recommendation for this INR range over lower ranges (such as 1.5-1.9), as lower targets significantly increase recurrent DVT risk. 2
Evidence Against Alternative INR Ranges
Lower INR ranges are dangerous and should be avoided:
Using an INR below 2.0 increases the relative risk of recurrent DVT by 3.25-fold, resulting in 24 additional DVT events per 1,000 patients. 2
Lower ranges may also increase pulmonary embolism risk (relative risk 5.0) and mortality (relative risk 2.0). 2
Historical INR targets below 2.0 (such as 1.7 or 1.8) lack validation for safety or efficacy and must be avoided. 2
Higher INR ranges provide no additional benefit:
INR ranges of 3.0-4.5 or higher are not recommended for standard DVT treatment, as they increase bleeding risk without improving efficacy. 2
Higher intensity anticoagulation (INR 3.1-4.0) is specifically recommended against for DVT. 4
Critical Initiation Requirements
Warfarin must be bridged with parenteral anticoagulation to prevent initial prothrombotic effects:
Start warfarin on the same day as parenteral therapy (LMWH, fondaparinux, or UFH). 1, 5
Continue parenteral anticoagulation for a minimum of 5 days AND until INR is ≥2.0 for at least 24 consecutive hours—both conditions must be met. 1, 3, 5
This bridging period is essential because warfarin initially creates a prothrombotic state before achieving therapeutic anticoagulation. 2
Failing to adequately bridge increases recurrent thrombosis risk substantially. 2
Monitoring and Maintenance
Aim for a time in therapeutic range (TTR) of 65-70% for optimal efficacy and safety. 3
Patients with TTR below 65% experience higher rates of stroke, systemic embolism, mortality, and major bleeding compared to those maintaining adequate TTR. 3
After initial stabilization, check INR weekly for 2-3 weeks, then extend to every 2-4 weeks once consistently stable. 5
For patients with consistently stable INRs, monitoring intervals can extend to 6-12 weeks. 5
Special Populations
Cancer-associated DVT:
LMWH monotherapy is preferred over warfarin for cancer patients when possible. 1, 5
If warfarin must be used in cancer patients, the same INR target of 2.0-3.0 applies, but more frequent monitoring is required due to chemotherapy drug interactions. 1, 5
Elderly patients (≥75 years):
- Some experts suggest a target INR of 2.0 with range 1.6-2.5 for atrial fibrillation patients to reduce bleeding risk, but this does not apply to DVT treatment where the standard 2.0-3.0 range remains appropriate. 3
Common Pitfalls to Avoid
Never use subtherapeutic INR targets: Targets like 1.5-1.9 dramatically increase recurrent thrombosis risk. 2, 4
Never discontinue parenteral therapy prematurely: Both the 5-day minimum AND therapeutic INR for 24 hours must be achieved. 1, 3
Never use excessive anticoagulation: INR above 5.0 becomes clinically unacceptable due to exponentially increasing bleeding risk. 6
Never assume INR adequacy without proper bridging: The INR may reach 2.0-3.0 before adequate depletion of all vitamin K-dependent clotting factors occurs. 5