Partial Thromboplastin Time
Rountree KM, and Lopez PP. "Partial Thromboplastin Time". StatPearls. Treasure Island (FL), StatPearls Publishing LLC. 2020.
Partial thromboplastin time (PTT) is the time it takes for a patient's blood to form a clot as measured in seconds. It is used to measure the activity of the intrinsic pathway of the clotting cascade. PTT tests the function of all clotting factors except VII (tissue factor) and XIII (fibrin stabilizing factor). PTT is commonly used in clinical practice to monitor patient response to unfractionated heparin infusion to target therapeutic anticoagulation, and as part of a "coagulation panel" to help elucidate causes of bleeding or clotting disorders.