What is a prothrombin time (PT) test?

A prothrombin time (PT) test measures the time it takes for the liquid portion of your blood to clot. This liquid portion of the blood is called plasma. Clotting refers to the formation of the blood and proteins into a solid mass to stop bleeding.

Sometimes this test is called an INR (International Normalized Ratio) or ProTime test.

Why is a prothrombin time (PT) test done?

The average time it takes for blood to clot is 10 to 14 seconds. If your blood clots more slowly or more quickly than that, you may have a clotting problem. If your healthcare provider suspects this, he or she may recommend a PT test.

The most common reason for PT tests is to monitor your blood levels if you are taking the blood-thinner warfarin.

Warfarin is used to prevent blood clots. Blood clots can cause serious conditions, such as deep venous thrombosis or pulmonary embolism.

Other reasons you may be given a PT test are to:

  • Check liver function
  • Discover the cause of abnormal bruising or bleeding
  • Check for signs of bleeding disorders that can cause bleeding issues, such as hemophilia

What does a PT test check for?

A PT test checks the speed at which your blood clots.

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