Prothrombin time (PT)

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Prothrombin time (PT) is a blood test that measures the time it takes for the liquid portion (plasma) of your blood to clot.

See also: Partial thromboplastin time (PTT)

PT; Pro-time

The health care provider uses a needle to take blood from one of your veins. The blood collects into an airtight container. You may be given a bandage to stop any bleeding. If you are taking a medicine called heparin, you will be watched for signs of bleeding.

The laboratory specialist will add chemicals to the blood sample and see how long it takes for the plasma to clot.

Your doctor may tell you to stop taking certain drugs before the test. For example, blood thinners can affect the results of this test.

Do not stop taking any medicine without first talking to your doctor.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

The PT is a broad screening test for many types of bleeding disorders. Your doctor may order this test if you have signs of a blood clotting disorder.

Review Date: 03/09/2007
Reviewed By: Mark Levin, MD, Hematologist and Oncologist, Newark, NJ. Review provided by VeriMed Healthcare Network.