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Prothrombin time (PT) Prothrombin time (PT) is a blood test that measures the time it takes for the liquid portion (plasma) of your blood to clot. A related blood test is partial thromboplastin time (PTT). A blood sample is needed. If you are taking ant blood-thinning medicines, you will be watched for signs of bleeding.
A prothrombin time (PT) test measures the amount of time it takes for your blood plasma to clot. Prothrombin, also known as factor II, is just one of many plasma proteins involved in the clotting process. Advertisement. Advertisement.