What is a normal blood INR level?

Normal international normalized ratio, or INR, levels for individuals who are not on anticoagulant medication range between 0.9 and 1.1. Patients who are on blood thinning medications typically have elevated INR levels between 2 and 3.5, according to the American Association for Clinical Chemistry.

Doctors derive a patient's INR from a prothrombin time test, which is a clinical blood test that measures the amount of time it takes for blood plasma to clot, as stated by MedlinePlus. Higher-than-normal INR levels indicate blood is clotting slower than expected, while lower levels indicate blood is clotting faster than desired, according to Mayo Clinic.