Overview coagulation Tests PT (extrinsic pathway) tests function of factors I II V VII X defect in any of these → ↑ PT 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 factor are synthesized in the liver PTT (intrinsic pathway) tests function of all factors EXCEPT VII XIII defect in any of these→ ↑ PTT XII also leads to defect in bradykinin activation best test to follow heparin therapy note also increases PT time Clinical Importance Hemophilia A/B Protein C/S deficiency Factor V Leiden Vitamin K deficiency Antithrombin activated by heparin deficiency