Therapeutic INR Level for Warfarin
For most patients on warfarin, the therapeutic INR target is 2.0-3.0, with a midpoint goal of 2.5. 1, 2, 3
Standard Target Ranges by Indication
Most Common Indications (INR 2.0-3.0)
The following conditions require an INR target of 2.0-3.0: 1, 2, 3
- Atrial fibrillation with stroke risk factors 1, 3
- Venous thromboembolism (deep vein thrombosis and pulmonary embolism) 1, 3
- Valvular heart disease (rheumatic mitral valve disease, bioprosthetic valves for first 3 months) 2, 3
- Post-cardioversion 2
Higher Intensity Anticoagulation (INR 2.5-3.5)
A more intensive target of 2.5-3.5 is required for: 1, 2, 3
- Mechanical prosthetic heart valves (all types, though some bileaflet valves in aortic position may use 2.0-3.0) 1, 2, 3
- Post-myocardial infarction patients at extremely high risk of stroke 1
- Mitral valve disease with prior embolic stroke (may require INR 3.0-4.5) 1
Critical Safety Thresholds
Subtherapeutic Anticoagulation
- INR <2.0 significantly increases thromboembolism risk and represents inadequate protection 1, 2
- Approximately 23-28% of INR measurements fall below 2.0 even in well-managed patients 4, 5
Supratherapeutic Anticoagulation
The bleeding risk increases exponentially as INR rises above the therapeutic range: 1, 6
- INR 4.0-5.0: Requires dose adjustment; withhold 1-2 doses and resume at lower dose 1, 2
- INR 5.0-9.0: Withhold warfarin; consider oral vitamin K 1-2.5 mg if bleeding risk factors present 1, 2
- INR >9.0: Give oral vitamin K 3-5 mg; expect INR reduction within 24-48 hours 1
- INR >5.0 becomes clinically unacceptable for bleeding risk 6
- Major hemorrhage risk is 4.4% within 14 days when INR >6.0 7
Monitoring Strategy
Initial Phase
- Check INR daily until therapeutic range achieved and sustained for 2 consecutive days 1, 2
- Then check 2-3 times weekly for 1-2 weeks 1, 2
- Then weekly for 1 month 1, 2
Maintenance Phase
- Once stable, extend monitoring intervals up to 4 weeks (some guidelines suggest up to 12 weeks for consistently stable patients) 1, 2
- Increase monitoring frequency during diet changes, medication changes, weight fluctuations, illness, or any bleeding signs 1
Common Pitfalls to Avoid
Do not target INR ranges below 2.0 (such as 1.5-2.0) without strong evidence, as this provides inadequate protection against thromboembolism 1
Recognize that INR instability is common: even in well-managed primary care settings, approximately 39% of INR values fall outside the therapeutic range 5
Elderly patients (>65 years) may require lower maintenance doses due to increased warfarin sensitivity 1
When INR >4.0 occurs, patients typically require one additional visit and approximately 3 weeks to return to therapeutic range 5
Avoid high-dose vitamin K (10 mg) for elevated INR without active bleeding, as this can cause warfarin resistance lasting up to one week; use lower doses (1-2.5 mg orally) instead 1