Partially activated thromboplastin time, abbreviated as aptt, is the time required to observe plasma clotting after the addition of activated partial thromboplastin reagent and calcium ions to the tested plasma, and it is the more sensitive and most commonly used screening test for the endogenous coagulation system. The normal range is 31-43 seconds, and a prolongation of more than 10 seconds compared to normal control values is considered abnormal. aptt prolongation is commonly seen in coagulation factors 12, 11, 9, 8, 10, 5, 2 and fibrinogen deficiency, while aptt is also a common test for monitoring common heparin and diagnosing lupus anticoagulant substances. aptt shortening is commonly seen in thrombotic disorders such as cerebral thrombosis, coronary artery disease, lower extremity venous thrombosis and pre-thrombotic states.