The normal international normalization ratio range for people who are not on blood-thinning medicines is 0.8 to 1.1, according to MedlinePlus. However, an INR of 2.0 and 3.0 is effective for patients who need full anticoagulation and are on blood-thinning medicines such as warfarin, notes Mayo Clinic.
An INR result that is greater than 1.1 for an individual who is not on anticoagulants means that his blood is clotting slower than desired. This may be indicative of bleeding disorders, liver disease or vitamin K deficiency. A prothrombin time test result that is not within the normal range for people taking blood-thinning medication may be caused by wrong medicine dosage, alcohol consumption and taking certain over-the-counter medicine, supplements and antibiotics, explains MedlinePlus. Certain foods that contain high levels of vitamin K, such as liver, green tea and soybean products, can also interfere with the results, notes Mayo Clinic.