Doctors order partial thromboplastin time, or PTT, tests to check the effectiveness of blood thinning medications or assess other blood clotting factors, reports WebMD. They may use the tests, which measure how long blood takes to clot, to look for reasons for abnormal bleeding or check for specific clotting problems, bleeding disorders or liver conditions. Doctors also order PTT tests as a safety precaution before proceeding with surgeries or other medical procedures that involve bleeding.
PTT tests analyze proteins and other factors involved in the blood clotting process known as the coagulation cascade, explains MedlinePlus. To get more accurate results, doctors may ask patients to stop taking aspirin, vitamin C, antihistamines and other medications that can affect the readings. Results may vary among labs due to different measurement techniques. Depending on the results and an evaluation of a patient's overall health, doctors may adjust dosages of blood thinning medications such as heparin, notes WebMD.
Abnormal values in PTT tests can indicate hemophilia, von Willebrand disease or other bleeding disorders caused by a lack of blood clotting factors, points out WebMD. They may also indicate diseases that cause blood to clot too easily in arteries and veins, such as lupus anticoagulant syndrome or antiphospholipid antibody syndrome.