International Normalized Ratio (INR) Targets: Venous Thromboembolism

International Normalized Ratio (INR) targets should only be used for the monitoring of warfarin. Warfarin is less commonly used for venous thromboembolism due to the advent of direct-acting oral anticoagulants (DOACs), which typically require no monitoring. Warfarin also requires bridging with low molecular weight heparin (LMWH) due to the delayed effects of getting to a therapeutic INR within the first few days of initiation. ^[1]  In cases where cost is a significant factor or DOACs are unavailable, the use of warfarin may be preferred. 

The guidelines below are based on the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines for Antithrombotic Therapy and Prevention of Thrombosis (ninth edition, 2012). ^[2]

Acute pulmonary embolism (PE) ^{[3, 4]}

International normalized ratio (INR) target (range)

• Standard: 2.5 (2.0-3.0)

• Unprovoked, infrequent INR checks: 1.5-1.9 after 3 months of standard therapy

Duration of therapy

• Transient, reversible risk factor: 3 months

• First episode, unprovoked

  • Low/moderate bleeding risk: Extended therapy

  • High bleeding risk: 3 months

• Recurrent, unprovoked

  • Low/moderate bleeding risk: extended therapy

  • High bleeding risk: 3 months

• Cancer: Extended therapy,  if recurrent venous thromboembolism (VTE) consider switching to LMWH ^[5]

Acute deep venous thrombosis (DVT) of the lower extremity

INR target (range)

• Standard: 2.5 (2.0-3.0)

Duration of therapy

• Transient, reversible risk factor: 3 months

• First episode, unprovoked, proximal

  • Low/moderate bleeding risk: Extended therapy

  • High bleeding risk: 3 months

• First episode, unprovoked, distal: 3 months (guidelines suggest serial imaging for 2 weeks rather than early anticoagulation for patients with isolated distal lower-extremity DVT who do not have severe symptoms or risk factors for extension)

• Recurrent, unprovoked

  • Low/moderate bleeding risk: Extended therapy

  • High bleeding risk: 3 months

• Cancer: Extended therapy if recurrent VTE consider LMWH ^[5]

Acute DVT of the upper extremity

INR target (range): 2.5 (2.0-3.0) ^[6]

Duration of therapy

• Axillary or more proximal: 3 months or more

• Distal: 3 months

• Central venous catheter (CVC) related: Until catheter is removed, or a minimum of 3 months

Acute DVT in children

INR target (range) ^[7]

• Standard: 2.5 (2.0-3.0)

• CVC related: 1.5-1.9 after 3 months of standard therapy

Duration of therapy

• Idiopathic, first episode: 6-12 months

• Idiopathic, recurrent: Lifelong therapy

• Reversible risk factor: Until risk factor has resolved, or a minimum of 3 months

• Cancer, thrombophilia: Until risk factor has resolved, or a minimum of 3 months

• CVC related: Until CVC is removed, or a minimum of 3 months