Most experts believe that International Normalized Ratio levels above 4 are dangerous, according to INRTracker. Normal INR levels in healthy individuals are usually between 0.9 and 1.3.
Patients on blood thinners such as Warfarin are expected to have INR levels ranging from 2 to 3; however, some doctors prefer levels ranging from 2.5 to 3.5, INRTracker reports. INR levels at or above 5 often require a dose of vitamin K, the antidote for Warfarin, to bring the level down.
INR levels are a measurement of how long blood takes to clot; bleeding risk increases when INR levels are high, INRTracker explains. Various factors affect INR levels, including the amount of dietary vitamin K the patient consumes. Doctors usually advise patients who are taking Warfarin to ingest the same amount of green leafy vegetables, which are high in vitamin K, every day.