Activated Partial Thromboplastin Time Partial Thromboplastin Time

Overview & Description

The partial thromboplastin time (PTT) test helps measure the ability of the blood to clot normally. It is very similar to the prothrombin time (PT) test. These two tests are often ordered together.

At least 12 different proteins are involved in clotting. The PTT and PT test each measure the function of some of these proteins.

Who is a candidate for the test?

This test may be done:

  • when a person has a bleeding problem
  • to monitor a person who is taking blood-thinning medicine
  • before surgery to make sure a person will not bleed too much during the operation
  • How is the test performed?

    A blood sample is usually taken from a vein on the forearm or hand. The skin over the vein is first cleaned with an antiseptic. Next, a strong rubber tube, or tourniquet, is wrapped around the upper arm. This restricts blood flow through the veins in the lower arm and causes them to enlarge.

    A small needle is gently inserted into a vein and the tourniquet is removed. Blood flows from the vein through the needle. It is collected in a syringe or vial. After the needle is withdrawn, the puncture site is covered to prevent bleeding. The blood sample is sent to a lab for testing.

    Preparation & Expectations

    What is involved in preparation for the test?

    Generally, no preparation is needed for this test. Because test preparation may vary, a person should ask his or her healthcare provider for specific instructions.

    Results and Values

    What do the test results mean?

    The normal range for a PT test depends on the standards of the lab. It generally falls between 25 to 45 seconds. Abnormally high PTT values may occur when a person:

  • is taking blood-thinning medicines, especially heparin
  • is taking other medicines, such as certain antibiotics, that interfere with the test
  • has severe liver disease
  • has disseminated intravascular coagulation (DIC), a complex blood disorder that occurs when clotting mechanisms are activated throughout the body
  • has certain inherited bleeding disorders, such as hemophilia
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  • Abnormally low values are usually not important. Occasionally they are a sign of widespread cancer.

    Article type: xmedgeneral