written by: Leigh A. Zaykoski•edited by: Leigh A. Zaykoski•updated: 10/31/2009
The PTT blood test, also known as the partial prothrombin time, is used to diagnose or monitor bleeding and clotting disorders. Learn more about the PTT blood test in this laboratory testing guide.
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This test is used along with the PT test to determine why someone has had a thrombotic episode or episode of bleeding. Thrombotic episodes are displays of the signs and symptoms of a blood clot in one of the veins or arteries. Because either type of episode can cause life-threatening complications, it's important that these tests are ordered and a diagnosis made. This test is also used in a panel of tests that are used to help determine why a woman has had several miscarriages. Surgeons may order this test to determine if someone has a tendency to bleed heavily during surgery.
If someone has already been diagnosed with a bleeding or clotting disorder, the PTT blood test can be used to monitor the effects of treatment. Heparin, an anticoagulant that is given to prevent or treat blood clots, may be administered intravenously. When this drug is given, its effects need to be monitored closely to prevent excessive bleeding episodes.
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This test requires that a sample of blood be drawn from a vein in the arm. This is a simple procedure that only takes a few minutes if there are no complications. You may feel lightheaded or faint after your blood is drawn. If this occurs, let the phlebotomist know you are experiencing these symptoms. You may be advised to rest before you can leave the laboratory. There is also the risk of bruising and bleeding associated with the needle stick. The blood sample is analyzed to determine how quickly and effectively the blood clots.
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Normal PTT blood test results usually indicate that there are no clotting problems. However, deficiencies of only one blood clotting factor may exist. These will not affect the PTT results until they are at least 30 percent below normal. Low levels of PTT may indicate that clotting factor VIII levels are elevated. This can occur as the result of trauma or acute tissue inflammation. Prolonged PTT indicates that clotting is delayed, and a bleeding disorder may be present. Clotting factors may be deficient, or the blood 's ability to clot may be impaired.
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Other blood tests may be used with the PTT test or after the PTT results have been received. You may be asked to have a platelet count or thrombin time testing done. Fibrinogen testing may also be done if PTT is prolonged. These tests are used to confirm or rule out bleeding and clotting disorders or other medical conditions that can affect PTT results.