What is a normal International Normalized Ratio (INR) range?

Normal INR Range

The normal INR range for individuals not on anticoagulation therapy is 0.8-1.2, while the therapeutic INR range for patients on warfarin therapy is typically 2.0-3.0, with a target of 2.5 to maximize time in therapeutic range and optimize outcomes. 1

Normal INR in Different Clinical Contexts

For Individuals Not on Anticoagulation

• Normal INR: 0.8-1.2
• Values in this range indicate normal blood clotting function
• INR values below 2.0 in non-anticoagulated patients do not predict bleeding risk 1

For Patients on Warfarin Therapy

The therapeutic range depends on the clinical indication:

1. Standard Anticoagulation (most indications including atrial fibrillation):

   • Target INR: 2.0-3.0 (aiming for 2.5) 1
   • This range provides optimal balance between preventing thromboembolism and avoiding bleeding

2. Mechanical Heart Valves:

   • Bileaflet or tilting disc valves: INR 2.5-3.5 2
   • Caged ball or caged disc valves: Higher target INR required 2
   • Patients with additional risk factors may need higher targets 3

Clinical Significance of INR Values

Subtherapeutic INR (<2.0 for patients on warfarin)

• Increased risk of thromboembolism/ischemic stroke 1
• INR <2.0 provides incomplete protection against stroke in atrial fibrillation 1

Supratherapeutic INR (>3.0 for standard indications)

• INR >3.0: Greater incidence of major bleeding 1
• INR >3.5: Significantly increased risk of intracranial hemorrhage 1
• INR >5.0: Bleeding risk increases exponentially 2
• INR >9.0: High risk of bleeding (11% in outpatients, 35% in inpatients on warfarin) 4

Time in Therapeutic Range (TTR)

The proportion of time spent within the therapeutic INR range is critically important:

• Target TTR: At least >65% 1
• Lower TTR associated with increased risks of:
  • Thromboembolism (HR 2.55; 95% CI, 1.61-4.03)
  • All-cause mortality (HR 2.39; 95% CI, 1.87-3.06)
  • Major bleeding (HR 1.54; 95% CI, 1.04-2.26) 1

Special Considerations

Elderly Patients (>75 years)

• May benefit from slightly lower target INR (2.0-2.5) to reduce bleeding risk, particularly intracranial hemorrhage 1, 2
• However, the conventional INR target of 2.0-3.0 is still recommended globally due to lack of robust evidence for lower targets 1

Optimal INR for Balancing Risks

Recent analysis of modern warfarin trials shows:

• INR between 2.0-2.5 provides the best balance between ischemic stroke and intracranial hemorrhage
• Risk only slightly increases between INR of 1.8 and 3.0 5
• U-shaped relationship exists between INR and all-cause mortality 5

Common Pitfalls in INR Interpretation

1. Misinterpreting single INR values: Random "one-off" INR values give little insight into anticoagulation quality; focus on TTR 1

2. Applying warfarin INR targets to non-warfarin contexts: INR was developed specifically for monitoring vitamin K antagonist therapy and has poor predictive value for bleeding in other contexts 1

3. Overreliance on INR in non-anticoagulated patients: INR does not predict bleeding risk in patients with liver disease, disseminated intravascular coagulation, or trauma 1

4. Inappropriate plasma transfusion: No high-quality evidence supports plasma transfusion for mildly abnormal INR values in non-bleeding patients 1

By maintaining INR within the appropriate therapeutic range and maximizing time in therapeutic range, clinicians can optimize outcomes by balancing the risks of thromboembolism and bleeding in patients requiring anticoagulation.