Overview Tests PT (extrinsic pathway) tests function of factors I II V VII X defect in any of these → ↑ PT e.g. vitamin K deficiency best test to follow warfarin therapy normalized as an INR (international normalized ratio) note also increases PTT time also used to measure hepatic function as most of the factors are synthesized in the liver PTT (intrinsic pathway) tests function of all factors EXCEPT VII XIII defect in any of these→ ↑ PTT best test to follow heparin therapy note also increases PT time