Prothrombin Time
(PT and INR)

Alternate Names

  • Pro-Time
  • International Normalized Ratio (INR)

PT is a measurement of the amount of time it takes for your blood to clot, which is an indication of both the amount of clotting factors present in the blood and how well they are working. Low levels of clotting factors will result in a longer-than-normal amount of time for blood clotting, and may be due to inherited deficiency of clotting factors, DIC (disseminated intravascular coagulation), large numbers of blood transfusions, liver disease, vitamin K deficiency, chronic alcohol abuse, aspirin toxicity, or cancer. PT is also used to monitor therapeutic effects of the blood-thinner Coumadin (warfarin). There are many medications that can affect prothrombin time. Values will vary according to the lab that is doing the testing. INR is a value that has been standardized between countries to ensure accurate and consistent reporting of blood levels.

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