What is the normal International Normalized Ratio (INR) range for a patient on Coumadin (Warfarin)?

From the Guidelines

The normal International Normalized Ratio (INR) range for a patient on Coumadin (Warfarin) is 2.0-3.0.

Rationale

• This range is recommended by multiple studies, including the European Society of Cardiology guidelines 1 and the American Heart Association/American College of Cardiology Foundation guide to warfarin therapy 1, as it achieves a balance between stroke risk with low INRs and an increasing bleeding risk with high INRs.
• The American Heart Association/American Stroke Association guideline for the prevention of stroke in patients with stroke or transient ischemic attack also recommends an INR target of 2.0-3.0 for patients with mechanical prosthetic heart valves 1.
• Additionally, the management of massive and submassive pulmonary embolism, iliofemoral deep vein thrombosis, and chronic thromboembolic pulmonary hypertension guideline recommends an INR target of 2.0-3.0 for patients with iliofemoral deep vein thrombosis 1.

Key Considerations

• The optimal INR range may vary depending on individual patient factors, such as age, comorbidities, and bleeding risk.
• Regular monitoring of INR levels is crucial to ensure that patients remain within the therapeutic range and to minimize the risk of bleeding or thromboembolic events.
• The use of pharmacogenetic testing, such as CYP2C9 and VKORC1 genotyping, may be considered in patients who are at high risk for bleeding or have difficulty maintaining a stable INR 1.

From the FDA Drug Label

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. For patients with a St. Jude Medical (St. Paul, MN) bileaflet valve in the aortic position, a target INR of 2.5 (range, 2.0 to 3.0) The results for WARIS II are provided in the following table: ... Warfarin target INR 2.8 to 4.2, ... or warfarin target INR 2.0 to 2. 5 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).

The normal International Normalized Ratio (INR) range for a patient on Coumadin (Warfarin) is 2.0 to 3.0. This range is the target for most treatment durations, including for patients with mechanical prosthetic heart valves and those with non-valvular atrial fibrillation. 2

From the Research

Normal International Normalized Ratio (INR) Range for Patients on Coumadin (Warfarin)

The normal INR range for patients on Coumadin (Warfarin) varies depending on the clinical condition being treated.

• For patients with nonvalvular atrial fibrillation, the recommended INR range is 2.0-3.0 3, 4.
• For patients with prosthetic heart valves, the target INR range is 2.5-3.5 for bileaflet or tilting disc valves, and a higher target INR is necessary for caged ball or caged disc valves 3.
• The risk of bleeding increases exponentially with INR and becomes clinically unacceptable once the INR exceeds 5.0 3.

Time in Therapeutic Range (TTR)

TTR is essential for the safety and efficacy of warfarin treatment.

• Studies have shown that maintaining a TTR above 70% is challenging, but achievable with a dedicated multi-faceted approach 5.
• The mean percent time with INR in the therapeutic range was 67% in one study, with 19% of INR values being <2.0 and 14% being >3.0 4.
• Factors such as frequency of INR visits per year, patient awareness of target INR, and duration of warfarin use can influence TTR 6.

Bleeding Risk

Bleeding is the main complication of warfarin therapy, even in patients with a therapeutic INR.

• Low factor IX levels can underestimate the level of anticoagulation in patients with an INR in the target range, increasing the risk of bleeding 7.
• Patients who bleed when their INR is in the target range may have defective thrombin generation related to a lower level of factor IX than expected 7.