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 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 (blood thinner) medicine. You need to have just enough to prevent clots. If the dosage is too high, you may bleed too easily. The test helps your provider find the right dosage of medicine.

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

How do I prepare for this test?

  • You may need to avoid taking medicine before the test. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Don't stop any of your regular medicines without first consulting with your healthcare provider.
  • Talk to your healthcare provider if you have any questions about the test.

How is the test done?

A small amount of blood is taken from a vein in your arm with a needle or by pricking your finger. The blood is collected and sent to a lab.

Having this test will take just a few minutes.

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. This may happen if you are taking the blood thinner warfarin, and it means that the warfarin 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
  • have an inherited blood disorder
  • have had a lot of heavy bleeding recently

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

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 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
  • when you need to be tested again
  • what lifestyle, diet, or other changes you might need to make

Written by Tom Richards, MD.
Published by RelayHealth.
© 2012 RelayHealth and/or its affiliates. All rights reserved.