Final answer:
To monitor anticoagulant therapy dosage, the PT/INR blood test is used, which measures the clotting time of blood and ensures the correct dosage of anticoagulants is administered.
Step-by-step explanation:
The blood test used to monitor anticoagulant therapy dosage is PT/INR (Prothrombin Time/International Normalized Ratio). This test measures the time it takes for blood to clot and compares it to a normal (control) value. A longer clotting time, indicated by a higher INR value, means that the blood is taking longer than usual to clot, which is an intended effect of anticoagulants like warfarin (Coumadin). The PT/INR test is crucial to ensure that the dosage of the anticoagulant is appropriate, as too high of a dose can increase the risk of bleeding, while too low of a dose may not provide sufficient anticoagulation.