International Normalized Ratio (INR) is a blood test that measures the time it takes for blood to clot. This test is usually administered to people taking anticoagulants or blood thinners.
The lower the INR number, the shorter it takes for blood to clot and the greater risk you have for blood clots. The higher the INR number, the longer it takes for blood to clot and the greater risk you have of bleeding. Most healthy people will have an INR of 0.9 - 1.3.1 Patients who are taking blood thinners such as Warfarin are usually considered therapeutic by their doctors when their INR is between 2.0 and 3.0. Sometimes depending on the condition a doctor might consider a patient therapeutic when their INR is between 2.5 and 3.5. However, it is generally considered dangerous to have an INR above 4.0. An INR above 5.0 may require a medical dose of vitamin K to bring the INR down to a therapeutic range.2
Types of INR Tests
An INR test is taken by drawing blood from the patient.
Many doctors will perform the test using a PT/INR meter. The meter functions similarly to a Diabetes meter where the patient places a drop of blood taken from the finger onto a test strip that is inserted into the machine. The INR results are usually provided within a few minutes.
Some patients will have their blood drawn by their healthcare provider and sent to a lab to test their INR. The INR results are usually provided within one-three days.
INR Test Frequency
Most patients will have numerous doctors visits and INR tests when they first begin taking blood thinners, typically ranging from 2-3 times a week. The reason for this is because blood thinners are very difficult to regulate because they interact with common foods, and because they are extremely dangerous if taken inappropriately.
Usually, after the patient becomes therapeutic (when the INR number stays consistently in a healthy range of 2.0 - 3.0 or 2.5 - 3.5) the patient can begin to reduce their number of doctors visits. Patients will still be required to see their doctor at regular, but less frequent intervals.
INR Fluctuation Causes
A patient will almost never know if their blood levels are too thin or thick without taking an INR test. A persons INR will go up and down depending on a variety of factors. The most common causes are diet.
Vitamin K is the antidote for blood thinners such as Warfarin (also known as Coumadin). Patients are usually discouraged from ingesting foods high in vitamin k such as green leafy vegetables. However, patients need to be mindful that it is not healthy to completely restrict Vitamin K intake either or else they could become Vitamin K deficient. The best method of maintaining a proper Coumadin diet is to ingest the same amount of Vitamin K each day/week.
Alcohol, exercise, over the counter medicines such as aspirin and vitamins, and other medications are all known to interfere with blood thinners and must be taken cautiously and consistently to limit spikes and dips in INR's.
Regulating Your INR
Maintaining a consistent INR is very difficult because blood thinners are extremely sensitive. The best method of regulating your INR is to monitor your diet, alcohol intake, drug dosages, exercise, and other medicines you take. INR Tracker is a free tool developed to help you do just that. Sign up today.
- Department of Health and Human Services, "2011.08.11 CR2412 Doylestown Health Care Center v. CMS." Last modified August 11, 2011. Accessed April 22, 2012. http://www.hhs.gov/dab/decisions/civildecisions/cr2412.pdf.
- British Columbia Medical Services Commission, "Warfarin therapy management." Last modified October 1, 2010. Accessed April 22, 2012. http://www.guideline.gov/content.aspx?id=24513.