# Thromboplastin --- **Thromboplastin** is a [[plasma|plasma protein]] that aids blood [[coagulation]] by catalyzing the conversion of **prothrombin** to **thrombin**. It is also known as the coagulation factor III, a tissue factor. It activates the extrinsic pathway during blood clotting. Thrombin goes on to activate to [[fibrin]] and other factors in the intrinsic pathway of of the [[coagulation|coagulation cascade]]. **Partial thromboplastin** is a phospholipid derivative of thromboplastin. In the lab partial thromboplastin is produced to measure the intrinsic pathway. [[partial and activated partial thromboplastin time|aPTT]] and [[partial and activated partial thromboplastin time|PTT]] are two types of medical tests used to characterize blood coagulation in intrinsic pathway. ___