This picture shows the extrinsic and intrinsic pathways of coagulation. The most important aspect of coagulation lies in its tests to differentiate between different types of hematologic diseases. There are two main tests to be used, the first is Prothrombin time (PT) which is used to test the extrinsic pathway. Normal PT is 10 to 13 seconds, PT tests the following factors I, II, V, VII, and X. Any defect in these factors will lead to increased PT. PT can aso be used to monitor warfarin therapy through INR. The second important test is Partial thromboplastin time (PTT) which is used to test intrinsic pathway. Normal PTT is 25-35 seconds. PTT tests the following factors VII, and XIII. Any defect in these factors will increase PTT. PTT can also be used to monitor heparin therapy and liver function.