What is a normal International Normalized Ratio (INR)?

From the Guidelines

A normal International Normalized Ratio (INR) is between 2.0 and 3.0.

INR Range

• The optimal target INR range for prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation is 2.0 to 3.0 1.
• This range is recommended for most atrial fibrillation patients, as it provides a balance between stroke risk with low INRs and an increasing bleeding risk with high INRs 1.
• For primary prevention in the very elderly, a target INR of 2.0 (target range 1.6 to 2.5) may be recommended to minimize bleeding risk 1.

Importance of INR Control

• Maintaining an INR within the therapeutic range is crucial, as low-intensity anticoagulation can lead to reduced stroke protection, and high-intensity anticoagulation can increase the risk of bleeding 1.
• Self-management of anticoagulation can help reduce INR variability and should be recommended for patients who can control their own anticoagulation 1.

Special Considerations

• For patients with mechanical prostheses, the target INR range may vary depending on the prosthesis type and patient-related risk factors, but generally ranges from 2.0 to 4.0 1.
• In patients with valvular heart disease, the target INR range may be higher, typically 2.0 to 3.0 or higher, depending on the specific condition and risk factors 1.

From the Research

Definition of International Normalized Ratio (INR)

• The International Normalized Ratio (INR) is a test used to measure blood clotting and is primarily used to monitor patients on warfarin or related oral anticoagulant therapy 2.
• The INR is calculated from the prothrombin time (PT) and allows for worldwide standardization of results 3.

Normal INR Range

• A normal INR range is typically considered to be between 0.9 and 1.1, but this can vary slightly depending on the laboratory and the specific test used 4.
• For patients on warfarin or other anticoagulant therapy, the target INR range is usually between 2.0 and 3.0, but this can vary depending on the individual patient's condition and the specific treatment goals 5.

Factors Affecting INR Results

• The INR result can be affected by various factors, including the type of thromboplastin reagent used, the instrument used to perform the test, and the international sensitivity index (ISI) value 6, 4.
• Interlaboratory variation and bias in INR results can be reduced by standardizing methods and using novel strategies, such as verification harmonization of local ISI and mean normal prothrombin time 5.

Clinical Significance of INR

• The INR is an important test for monitoring patients on anticoagulant therapy and for diagnosing coagulation disorders 2, 3.
• An elevated INR can indicate an increased risk of bleeding, while a low INR can indicate an increased risk of thrombosis 2.