Prothrombin Time

International Normalized Ratio (INR), Pro Time, PT (Prothrombin Time)

Why It Is Done

Prothrombin time (PT) is measured to:

• Find a cause for abnormal bleeding or bruising.
• Check to see if blood-thinning medicine, such as warfarin (Coumadin), is working. If the test is done for this purpose, a PT may be done every day at first. When the correct dose of medicine is found, you will not need so many tests.
• Check for low levels of blood clotting factors. The lack of some clotting factors can cause bleeding disorders such as hemophilia, which is passed in families (inherited).
• Check for a low level of vitamin K. Vitamin K is needed to make prothrombin and other clotting factors.
• Check how well the liver is working. Prothrombin levels are checked along with other liver tests, such as aspartate aminotransferase and alanine aminotransferase.
• Check to see if the body is using up its clotting factors so quickly that the blood cannot clot and bleeding does not stop. This may mean the person has disseminated intravascular coagulation (DIC).

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Author:	Robin Parks, MS	Last Updated: September 15, 2008
Medical Review:	Anne C. Poinier, MD - Internal Medicine Brian Leber, MDCM, FRCPC - Hematology
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