PT is measured in seconds. Most of the time, results are given as what is called INR (international normalized ratio).
If you are not taking blood thinning medicines, such as warfarin, the normal range for your PT results is:
11 to 13.5 seconds
INR of 0.8 to 1.1
If you are taking warfarin to prevent blood clots, your provider will most likely choose to keep your INR between 2.0 and 3.0.
Ask your provider what result is right for you.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
If you are not taking blood thinning medicines, such as warfarin, an INR result above 1.1 means your blood is clotting more slowly than normal. This may be due to:
Bleeding disorders, a group of conditions in which there is a problem with the body's blood clotting process.
If you are taking warfarin to prevent clots, your provider will most likely choose to keep your INR between 2.0 and 3.0:
Depending on why you are taking the blood thinner, the desired level may be different.
Even when your INR stays between 2.0 and 3.0, you are more likely to have bleeding problems.
INR results higher than 3.0 may put you at even higher risk for bleeding.
INR results lower than 2.0 may put you at risk for developing a blood clot.
A PT result that is too high or too low in someone who is taking warfarin (Coumadin) may be due to:
The wrong dose of medicine
Taking certain over-the-counter (OTC) medicines, vitamins, supplements, cold medicines, antibiotics, or other medicines
Eating food that changes the way the blood-thinning medicine works in your body
Your provider will teach you about taking warfarin (Coumadin) the proper way.
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
Fainting or feeling lightheaded
Hematoma (blood accumulating under the skin)
Multiple punctures to locate veins
Infection (a slight risk any time the skin is broken)
This test is often done on people who may have bleeding problems. Their risk of bleeding is slightly higher than for people without bleeding problems.
Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.