Final answer:
Heparin therapy is primarily monitored by the aPTT (Activated Partial Thromboplastin Time), which is a test used to assess the intrinsic pathway of the coagulation system that heparin affects.
Step-by-step explanation:
Heparin therapy is monitored by daily measurement of the c) aPTT (Activated Partial Thromboplastin Time). The aPTT test is used to assess the intrinsic pathway of the coagulation cascade, which is the main pathway affected by heparin. Heparin is a short-acting anticoagulant that is used to prevent and treat blood clots by inhibiting the conversion of prothrombin (factor II) into thrombin, thereby preventing the formation of a thrombus.
While other tests like the platelet count, INR (International Normalized Ratio), and Prothrombin Time (PT) are also used to monitor coagulation status, they are not the primary tests for monitoring heparin therapy. INR is typically used to monitor warfarin therapy which affects the extrinsic pathway. Heparin's effect is best monitored with an aPTT test because it is designed to evaluate the intrinsic and common pathways of coagulation, both of which are affected by heparin.