Final answer:
Warfarin therapy is monitored using the International normalized ratio (INR), derived from Prothrombin Time (PT), which measures how long it takes for blood to clot and helps tailor the medication dosage.
Step-by-step explanation:
Coumadin (warfarin) therapy is closely monitored through coagulation tests, particularly by measuring the International normalized ratio (INR). The INR is a standardized way to measure how long it takes the blood to clot. It is crucial for adjusting warfarin dosage to avoid risks of overdose and to ensure the treatment is effective. Other tests such as Prothrombin Time (PT) also play a role, as PT is the base test from which INR is derived. However, tests like Activated Partial Thromboplastin Time (aPTT), Complete Blood Count (CBC), and other specific assays may not directly monitor warfarin therapy but can still provide relevant information about the patient's hematologic system and general health status.