A partial thromboplastin time (PTT) test is a blood test that measures the time it takes for a blood clot to form. The test is used to evaluate the function of the blood clotting system, which helps prevent bleeding and promotes healing when the body is injured.

The PTT test is typically performed by drawing a small sample of blood from a vein in the arm, using a needle and a tube. The sample is then placed in a special machine that measures the time it takes for the blood to clot.

Normal PTT levels vary depending on the laboratory and the specific method used to perform the test, but generally range from 25 to 35 seconds. Abnormal PTT levels may indicate a variety of medical conditions, including bleeding disorders, liver disease, or the use of certain medications that affect blood clotting.

PTT tests are often ordered when a person has symptoms that may be related to a bleeding disorder or when a person is taking a medication that affects blood clotting. The test is used to help diagnose and monitor medical conditions and to assess the effectiveness of treatment. PTT tests may also be ordered along with other blood tests, such as prothrombin time (PT) tests, to evaluate the function of the blood clotting system.