PT and INR Blood Test (Bleeding Test)

What is the PT and INR test?

The PT and INR blood test measures the time it takes your blood to form a clot. Other names for the PT test are prothrombin time and pro time. INR stands for international normalized ratio.

Why is this test done?

The PT/INR test is usually done when you are taking a blood thinner (anticoagulant) medicine, such as warfarin (Coumadin), to prevent blood clots. Clots can block blood vessels and possibly cause a heart attack or stroke. This test measures the effect of the anticoagulant. If the dosage is too high, you may bleed too easily and if itâ€™s too low, your blood may clot too easily. The test helps your healthcare provider find the right dosage of medicine.

The PT test may also be done to diagnose a bleeding disorder if you have abnormal bleeding or clotting.

How do I prepare for this test?

You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Ask your provider before stopping any of your regular medicines.
Talk to your healthcare provider if you have any questions about the test.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the results of the test.

What does the test result mean?

A PT/INR value higher than normal means your blood is taking longer than normal to form a clot. If you are taking a blood thinner, it means that the medicine is working.

If you are not taking a blood thinner and your values are higher than normal, you may:

Have liver disease
Need more vitamin K (vitamin K is important for the formation of blood clots)
Have an inherited blood disorder
Have had a lot of heavy bleeding recently

What if my test results are not normal?

Test results are only one part of a larger picture that takes into account your medical history, physical exam, and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your result and ask questions, such as:

If you need more tests
What kind of treatment you might need
What lifestyle, diet, or other changes you might need to make

Developed by RelayHealth.

Adult Advisor 2015.1 published by RelayHealth.
Last modified: 2013-10-18
Last reviewed: 2013-10-10

This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.

PT and INR Blood Test (Bleeding Test): References

Kids Health, reviewed by Steven Dowshen, MD on 3/11. Accessed 3/4/2014 – http://kidshealth.org/parent/system/medical/test_pt.html#

Patient.co.uk, Bleeding Disorders, no author or date listed. Accessed 3/5/2014 – http://www.patient.co.uk/doctor/bleeding-disorders

Algorithmic Selection and Interpretation of Diagnostic Tests, By R. Douglas Collins, MD, FACP. Williams and Wilkins. The Washington Manual of Medical Therapeutics, 29th edition, Charles F. Carey et al, Lippincott-Raven.

Labtestsonline.org. PT and INR. 5/2012. Accessed 9/2013 from http://labtestsonline.org/understanding/analytes/pt/.