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]
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
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