Prothrombin time test

A prothrombin time test measures how quickly your blood clots. Sometimes called a pro time test or PT test, a prothrombin time test uses a sample of your blood.

Prothrombin is a protein produced by your liver that helps your blood to clot. When you bleed, a series of chemicals (clotting factors) activate in a stepwise fashion. The end result is a clot which stops the bleeding. One step in the process is prothrombin turning into another protein called thrombin. The prothrombin time test measures how well the clotting process works and how long it takes to occur.

Why it's done Risks What you can expect Results

If you take a blood-thinning medication such as warfarin to prevent clots from forming, your doctor will recommend a prothrombin time test to monitor the medication's effectiveness. It can also be ordered to:

  • Detect a bleeding disorder
  • Diagnose liver problems
  • Screen people having surgery for unrecognized bleeding problems

A variation of the prothrombin time test is part of a test series called model for end-stage liver disease (MELD) used to assess the severity and priority of people waiting for liver transplants.

If your doctor suspects you may have liver problems, you may undergo additional testing to assess the health of your liver, such as liver enzyme tests. If your doctor suspects you may have a bleeding disorder, you may undergo additional clotting-function tests.

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