The
partial thromboplastin time (PTT) or
activated partial thromboplastin time (
aPTT or
APTT) is a medical test that characterizes
blood coagulation. Apart from detecting abnormalities in blood clotting, it is also used to monitor the treatment effects with
heparin, a major
anticoagulant. PTT is a performance indicator of the efficacy of both the "intrinsic" (now referred to as the
contact activation pathway) and the common coagulation pathways. It is used in conjunction with the
prothrombin time (PT) which measures the
extrinsic pathway.
Kaolin cephalin clotting time (KccT) is a historic name for the activated partial thromboplastin time.