In atrial fibrillation, what is the target INR range for most patients taking warfarin to reduce stroke risk?

• A. INR 2.0 to 3.0 (some high-risk 2.5 to 3.5)
• B. INR 1.0 to 2.0
• C. INR 3.0 to 4.0
• D. INR 1.5 to 2.5

Answer: (A)

Warfarin works by thinning the blood to prevent stroke-causing clots in atrial fibrillation, and the level of thinning is guided by the INR. The most commonly targeted range is 2.0 to 3.0 because this balance provides strong protection against stroke while keeping bleeding risk at an acceptable level. An INR below 2.0 means the blood isn’t thin enough, so stroke risk remains higher. An INR above 3.0 increases the chance of serious bleeding. In some high-risk patients, a slightly higher target like 2.5 to 3.5 may be used, but for most patients the standard aim is 2.0 to 3.0.