What is a normal International Normalized Ratio (INR) range for an individual not on anticoagulation therapy?

Normal INR Range

For individuals not on anticoagulation therapy, the normal INR range is 0.8 to 1.2, with values up to 1.3 generally considered within normal limits. 1

Understanding Normal INR Values

The INR was specifically designed and validated only for monitoring vitamin K antagonist (warfarin) therapy, not as a general screening test for coagulopathy or bleeding risk in patients not taking anticoagulants. 2 This is a critical distinction that is widely misunderstood in clinical practice.

Standard Reference Ranges

• Normal prothrombin time (PT) is 11-13.5 seconds, which corresponds to a PT ratio <1.4 times the normal control value. 1
• Normal INR for individuals not on warfarin is typically 1.0-1.3, with 1.0 representing the theoretical ideal where the patient's PT equals the laboratory's mean normal PT. 1
• An INR of 1.4 represents only minimal elevation above the upper limit of normal and falls within acceptable laboratory variation in many institutions. 1

Clinical Context: When INR Values Are Meaningful

For Patients on Warfarin Therapy

• The therapeutic INR range is 2.0-3.0 for most indications including atrial fibrillation, deep vein thrombosis, and pulmonary embolism. 2, 3
• Higher targets of 2.5-3.5 are used for mechanical prosthetic heart valves. 3
• INR values below 2.0 are subtherapeutic and increase thrombosis risk, while values above 3.0 increase bleeding risk. 2
• The risk of major bleeding becomes exponentially elevated when INR exceeds 5.0, and values above 10.0 represent a medical emergency. 3, 4

For Patients NOT on Warfarin

There is no high-quality evidence that INR values predict bleeding risk in patients not taking vitamin K antagonists. 2 This applies across multiple clinical scenarios:

• In liver disease: INR does not predict bleeding risk despite its use in the MELD score. 2
• In perioperative settings: A systematic review found weak or no association between pre-procedural INR and bleeding in 78 out of 79 studies assessed. 2
• In trauma and critical illness: INR is a poor predictor of factor levels and bleeding risk. 2
• In disseminated intravascular coagulation: INR does not reliably predict coagulation factor activity. 2

Common Clinical Pitfalls

Misuse of INR Targets Below 2.0

INR targets such as 1.5,1.7, or 1.8 commonly used in clinical practice lack any scientific validation. 2 These values likely originated from historical PT ratio ranges at institutions using non-standardized thromboplastins before INR was introduced, and they carried over into modern practice without objective validation for bleeding prediction. 2

Inappropriate Plasma Transfusion

Randomized trials show no reduction in bleeding when prophylactic plasma is given to correct mildly elevated INR values in patients not on warfarin. 2 Plasma infusion does not meaningfully change INR values below 1.5 and only minimally impacts values below 2.0. 2

Practical Algorithm for INR Interpretation

Step 1: Determine anticoagulation status

• If on warfarin → Use INR to guide therapy (target 2.0-3.0 for most indications). 2, 3
• If NOT on warfarin → INR has limited clinical utility for bleeding risk assessment. 2

Step 2: For patients NOT on warfarin with elevated INR

• Investigate underlying causes: liver disease, vitamin K deficiency, consumptive coagulopathy, medication effects. 2
• Do NOT use arbitrary INR thresholds (like 1.5 or 1.7) to guide transfusion decisions. 2
• Consider viscoelastic testing (TEG/ROTEM) if available for more comprehensive coagulation assessment. 2

Step 3: For pre-procedural assessment

• A PT ratio or INR >1.4 is generally considered a relative contraindication to invasive procedures. 1
• However, this threshold lacks strong validation in patients not on anticoagulants. 2