What is the target International Normalized Ratio (INR) for adults with pulmonary embolism (PE)?

Target INR for Pulmonary Embolism in Adults

For adults with pulmonary embolism treated with warfarin, the target INR should be maintained between 2.0 and 3.0 (target 2.5). 1, 2

Evidence-Based Recommendation

The American Society of Hematology 2020 guidelines provide a strong recommendation for using an INR range of 2.0 to 3.0 over a lower INR range for patients with venous thromboembolism (including PE) who use a vitamin K antagonist. 1 This recommendation is echoed consistently across multiple high-quality guidelines, including the British Thoracic Society 1 and American Heart Association statements. 1

Therapeutic Range Details

• The INR should be maintained between 2.0 and 3.0 throughout the entire treatment period for PE. 1, 3, 2
• This range applies whether the PE is provoked or unprovoked, first episode or recurrent. 1
• The same target range (2.0-3.0) applies to PE arising from venous thrombosis or right atrial thrombus in patients with congenital heart disease. 1

Bridging with Heparin

• Continue heparin (unfractionated or low molecular weight) for at least 5 days after starting warfarin AND until the INR has been ≥2.0 for at least 24-48 hours. 1, 3, 2, 4
• Both conditions must be met before discontinuing heparin—the 5-day minimum duration alone is insufficient. 2, 4
• For unfractionated heparin, use weight-based dosing: 80 IU/kg IV bolus followed by 18 IU/kg/hour continuous infusion, targeting an aPTT of 1.5-2.5 times control (45-75 seconds). 1, 4

Warfarin Initiation and Monitoring

• Begin warfarin at 5-10 mg daily for the first 2 days, then adjust based on INR. 1, 3
• Initial INR monitoring should occur every 1-2 days until stable in the therapeutic range. 1, 3, 2
• Once stable, continue regular monitoring to maintain the 2.0-3.0 range. 3

Critical Pitfalls to Avoid

Subtherapeutic anticoagulation is a major risk factor for recurrent PE. Research demonstrates that 42% of patients who developed breakthrough PE on warfarin had at least one subtherapeutic INR (<2.0) in the 14 days preceding their event. 5 Additionally, patients presenting with PE while on warfarin who had an admission INR <2.5 had significantly increased long-term all-cause mortality compared to those with INR ≥2.5 (adjusted HR 2.51,95% CI 1.08-5.86). 6

• Never discontinue heparin before both the 5-day minimum AND achievement of therapeutic INR for 24-48 hours. 2, 4
• Do not use lower INR targets (such as 1.5-2.0)—the 2.0-3.0 range is superior for both efficacy and safety. 1, 2
• Avoid large loading doses of warfarin; start with 5-10 mg daily and adjust based on response. 1, 2
• Ensure close monitoring during the first weeks of therapy when INR values are most unstable. 1, 3

Special Considerations

For patients with pulmonary hypertension and in situ thrombosis, the target INR is usually in the lower range of 2.0-3.0, though the risk of long-term anticoagulation is higher in this population. 1 However, the standard 2.0-3.0 range remains the target even in these complex cases.

Patients presenting with PE despite therapeutic anticoagulation (INR 2.0-3.0) represent a challenging subset with increased risk of death from recurrent PE (HR 4.43,95% CI 1.36-14.42). 6 These patients often require a change in anticoagulation strategy, with most receiving injectable anticoagulants to replace or supplement warfarin. 5