Definition
By Mayo Clinic staffA prothrombin time test measures how quickly your blood clots. A prothrombin time test, sometimes called a pro time test or PT test, uses a sample of your blood.
Prothrombin is a protein produced by your liver that helps your blood to clot. During the clotting process — such as might occur when you get a cut — prothrombin turns into another substance called thrombin. The prothrombin time test measures the time it takes for this to occur, causing your blood to clot.
If you take a blood-thinning medication, your doctor may recommend a prothrombin time test to monitor the medication's effectiveness. A prothrombin time test, along with other tests, is also used to monitor liver function.
- Prothrombin time (PT). In: Ferri FF. Ferri's Clinical Advisor 2011. Philadelphia, Pa.: Mosby; 2010. http://www.mdconsult.com/book/player/book.do?method=display&type=aboutPage&decorator=header&eid=4-u1.0-B978-0-323-05610-6..C2009-0-38600-6--TOP&isbn=978-0-323-05610-6&uniq=210978719. Accessed July 22, 2010.
- Pratt DS. Liver chemistry and function tests. In: Feldman M, et al. Sleisinger and Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa.: Saunders; 2010. http://www.mdconsult.com/book/player/linkTo?type=bookHome&isbn=978-1-4160-6189-2&eid=4-u1.0-B978-1-4160-6189-2..X0001-7--TOP&uniq=200844987-3. Accessed July 22, 2010.
- PT and INR. Lab Tests Online. http://www.labtestsonline.org/understanding/analytes/pt/glance.html#. Accessed July 22, 2010.
- Laboratory reference values. Prothrombin time. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2010.

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