Target INR Range for Warfarin Therapy
For most patients on warfarin, the target INR range is 2.0-3.0, with a midpoint target of 2.5. 1, 2
Standard Therapeutic Ranges by Indication
The target INR varies based on the specific clinical indication:
Most Common Indications (INR 2.0-3.0)
- Atrial fibrillation requires INR 2.0-3.0 for stroke prevention 1, 2
- Venous thromboembolism (deep vein thrombosis and pulmonary embolism) requires INR 2.0-3.0 3, 2, 4
- Tissue heart valves require INR 2.0-3.0 3
- Prevention of systemic embolism requires INR 2.0-3.0 3
- Bileaflet mechanical valve in aortic position requires INR 2.0-3.0 2, 4
Higher Intensity Indications (INR 2.5-3.5)
- Mechanical prosthetic heart valves (high-risk types, including tilting disk valves and bileaflet valves in mitral position) require INR 2.5-3.5 1, 2, 4
- Acute myocardial infarction with left ventricular thrombus requires INR 2.5-3.5 3
- Patients at extremely high risk of stroke may require INR 2.5-3.5 1
Critical Safety Thresholds
Understanding the boundaries of safe anticoagulation is essential:
- Subtherapeutic anticoagulation (INR <2.0) significantly increases the risk of thromboembolism and provides inadequate protection 1, 4
- INR values exceeding 4.0 provide no additional therapeutic benefit and substantially increase bleeding risk 2, 4
- The risk of bleeding increases exponentially when INR exceeds 5.0, becoming clinically unacceptable at this level 4, 5
- INR >6.0 carries an 8.8% risk of abnormal bleeding and 4.4% risk of major hemorrhage within 14 days 5
Monitoring Frequency
The frequency of INR monitoring should follow this algorithmic approach:
Initial Phase:
- Check INR daily until therapeutic range is reached and sustained for 2 consecutive days 1
- Then check 2-3 times weekly for 1-2 weeks 1
- Then check weekly for 1 month 1
Maintenance Phase:
- Once stable, monitoring intervals can be extended up to every 4 weeks 1, 6
- More frequent monitoring is required during diet changes, weight fluctuations, medication changes, illness, or any signs of bleeding 1
Common Pitfalls to Avoid
Do not target INR ranges below 2.0 without strong evidence, as this leads to inadequate protection against thromboembolism 1, 4. While some benefit may remain at INR 1.5-1.9 in atrial fibrillation, maximum efficacy requires INR >2.0 4.
Avoid loading doses when initiating warfarin therapy, as they increase complications without providing more rapid protection 2, 6. Instead, start with 2-5 mg daily (or 2-4 mg in elderly patients) 2, 6.
Do not use INR to monitor other anticoagulants. INR was specifically designed and validated only for warfarin (vitamin K antagonist) monitoring and should not be used for unfractionated heparin, direct oral anticoagulants like rivaroxaban, or to assess bleeding risk in patients not taking warfarin 7.
Special Populations
Elderly patients (>75 years) may require lower maintenance doses due to increased sensitivity and may benefit from a slightly lower target INR of 2.0-2.5 in atrial fibrillation to reduce intracranial bleeding risk 1, 4.
Patients with mechanical heart valves require individualized targets based on valve type and position, with caged ball or caged disk valves requiring INR 2.5-3.5 plus aspirin 75-100 mg daily 2.