Therapeutic INR Range for Warfarin
For most patients on warfarin, the therapeutic INR range is 2.0-3.0, with a target of 2.5. 1, 2, 3
Standard INR Targets by Clinical Indication
Most Common Indications (INR 2.0-3.0)
The following conditions require an INR range of 2.0-3.0 with a target of 2.5: 1, 2, 3
- Atrial fibrillation (non-valvular) with stroke risk factors 1, 3
- Venous thromboembolism including deep vein thrombosis (DVT) and pulmonary embolism (PE) 1, 3
- Valvular heart disease with atrial fibrillation 2, 3
- Rheumatic mitral valve disease with history of embolism 2
- Dilated cardiomyopathy 2
- Bioprosthetic heart valves (first 3 months post-insertion) 2
Higher Intensity Anticoagulation (INR 2.5-3.5)
A higher target INR range of 2.5-3.5 is required for: 1, 2, 3
- Mechanical heart valves (particularly mitral position or older ball/cage models) 4, 1, 3
- Post-myocardial infarction patients at extremely high risk of stroke 1
- Bileaflet or tilting disc prosthetic valves 3, 5
Special High-Risk Situations (INR 3.0-4.5)
For mitral valve disease with prior embolic stroke, an INR of 3.0-4.5 may be indicated 4
Critical Safety Thresholds
Subtherapeutic Anticoagulation
- INR <2.0 significantly increases thromboembolism risk and represents inadequate protection for most indications 1, 2
- Approximately 23% of INR measurements fall below 2.0 even in experienced warfarin users 6
Supratherapeutic Anticoagulation
- Bleeding risk increases exponentially when INR exceeds 4.0 1, 5
- INR >5.0 carries clinically unacceptable bleeding risk 5
- Among hospitalized patients with INR >9, bleeding occurs in 35% and mortality reaches 17% 7
Monitoring Strategy
Initial Phase
- Check INR daily until therapeutic range is reached and sustained for 2 consecutive days 1, 2
- Then monitor 2-3 times weekly for 1-2 weeks 4, 1, 2
- Followed by weekly monitoring for 1 month 4, 1, 2
Maintenance Phase
- Once stable, monitoring intervals can extend up to 4 weeks (or even 12 weeks for consistently stable patients) 1, 2
- More frequent monitoring is mandatory during: 4, 2
- Medication changes (especially antibiotics)
- Diet alterations or weight changes
- Intercurrent illness or fever
- Any indication of bleeding
Management of Out-of-Range INR
Mild Elevation (INR 3.0-5.0)
- Withhold one dose or reduce dosage if no bleeding present 4
- Resume at lower dose when INR approaches therapeutic range 4, 1
Moderate Elevation (INR 5.0-9.0)
Severe Elevation (INR >9.0)
- Give oral vitamin K 3-5 mg with expected INR reduction within 24-48 hours 1
- For hospitalized patients, withholding warfarin or vitamin K alone may be ineffective—plasma infusion immediately reduces INR and may be necessary 7
Life-Threatening Bleeding
- Administer vitamin K 10 mg by slow IV infusion over 30 minutes 1
- Plus fresh frozen plasma or prothrombin complex concentrate 1
- Note: High-dose vitamin K (10 mg) can cause warfarin resistance lasting up to one week 1
Common Pitfalls to Avoid
- Never target INR <2.0 without strong evidence—this lacks objective validation and provides inadequate thromboembolism protection 1, 2
- Do not use INR to assess bleeding risk in patients NOT taking warfarin—INR was specifically designed and validated only for vitamin K antagonist monitoring 8
- Avoid inconsistent vitamin K intake through diet, as this causes INR fluctuations 1
- Do not assume elderly patients need lower INR targets—they require the same therapeutic range but may need lower maintenance doses due to increased sensitivity 1
- Recognize that approximately 39% of INR values remain out of range even in experienced warfarin users, requiring vigilant monitoring 6