What are the normal International Normalized Ratio (INR) values?

From the Guidelines

The normal INR value for a healthy person not on anticoagulant therapy is between 0.8 and 1.2, while for patients on warfarin therapy, the target INR range is typically between 2.0 and 3.0 for most indications, such as atrial fibrillation, deep vein thrombosis, or pulmonary embolism, as recommended by the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1. For patients with mechanical heart valves or recurrent systemic embolism, a higher target range of 2.5 to 3.5 may be recommended, as suggested by the guidelines on the management of valvular heart disease by the European Society of Cardiology 1. The target INR range may also vary based on the type and location of the prosthesis, with some prostheses requiring a higher or lower target INR range, as outlined in the guidelines on the management of valvular heart disease 1. It is essential to note that INR values above the target range indicate an increased risk of bleeding, while values below the target range suggest inadequate anticoagulation and potential risk of clotting, as highlighted in the AAGBI guidelines: the use of blood components and their alternatives 2016 1. Some key points to consider when managing anticoagulation therapy include:

• The INR should be determined at least weekly during initiation of antithrombotic therapy and at least monthly when anticoagulation is stable, as recommended by the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1.
• For patients with nonvalvular AF unable to maintain a therapeutic INR level with warfarin, use of a direct thrombin or factor Xa inhibitor is recommended, as suggested by the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1.
• Bridging therapy with unfractionated heparin or low-molecular-weight heparin may be recommended for patients with AF and a mechanical heart valve undergoing procedures that require interruption of warfarin, as outlined in the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1. The INR is a standardized measurement that evaluates the extrinsic pathway of blood coagulation by measuring how long it takes blood to clot, specifically assessing the function of factors II, VII, and X, which are vitamin K-dependent clotting factors affected by warfarin therapy, as explained in the AAGBI guidelines: the use of blood components and their alternatives 2016 1. Overall, the management of anticoagulation therapy requires careful consideration of the individual patient's risk factors, the type and location of the prosthesis, and the target INR range, as well as regular monitoring of the INR to minimize the risk of bleeding and clotting, as recommended by the guidelines on the management of valvular heart disease by the European Society of Cardiology 1.

From the FDA Drug Label

For patients with a first episode of DVT or PE who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested For patients with a first episode of DVT or PE who have documented deficiency of antithrombin, deficiency of Protein C or Protein S, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels (>90th percentile of normal), treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis The risk-benefit should be reassessed periodically in patients who receive indefinite anticoagulant treatment.12,20 The dose of warfarin should be adjusted to maintain a target INR of 2.5 (INR range, 2.0 to 3.0) for all treatment durations. Atrial Fibrillation Five recent clinical trials evaluated the effects of warfarin in patients with non-valvular atrial fibrillation (AF). Meta-analysis findings of these studies revealed that the effects of warfarin in reducing thromboembolic events including stroke were similar at either moderately high INR (2.0-4.5) or low INR (1.4-3. 0). An INR of greater than 4. 0 appears to provide no additional therapeutic benefit in most patients and is associated with a higher risk of bleeding.

The normal INR values are not explicitly stated in the provided text for a healthy individual not taking warfarin. However, for patients on warfarin therapy, the target INR range is typically between 2.0 and 3.0 for most indications, and 2.5 to 3.5 or 3.0 to 4.0 for certain conditions such as mechanical heart valves or high-risk myocardial infarction patients, respectively. 2

From the Research

Normal INR Values

• The normal INR value range is typically between 2.0 and 3.0 for most patients on long-term oral anticoagulation therapy 3.
• This range may vary depending on the underlying indication for treatment and patient-level characteristics.
• For patients with mechanical heart valves, the target INR range may be higher, typically between 2.5 and 3.5 3.

Factors Affecting INR Values

• Vitamin K intake can affect INR values, and patients on warfarin therapy may have low plasma vitamin K levels 4.
• Other factors such as warfarin dose, regimen intensity, and interacting medications can also impact INR results 5.
• Timing of fresh frozen plasma administration can affect rapid correction of coagulopathy in warfarin-related intracerebral hemorrhage 6.

INR Monitoring and Management

• Point-of-care (POC) INR monitoring devices can provide immediate INR results, allowing for more rapid medication adjustments 3.
• POC INR monitoring can improve anticoagulation control, reduce thromboembolic events, and increase patient satisfaction 3.
• Regular INR monitoring is crucial to ensure that patients on warfarin therapy remain within the therapeutic range and minimize the risk of complications 3, 5.