Final answer:
The two lab tests used to monitor Coumadin therapy are PT (Prothrombin Time) and aPTT (Activated Partial Thromboplastin Time), with INR being a standardized measure for PT.
Step-by-step explanation:
The two laboratory tests used to monitor Coumadin therapy are PT (Prothrombin Time) and INR (International Normalized Ratio), a standardized version of PT. These tests assess the anticoagulant effects of Coumadin, also known as warfarin, by measuring the time it takes for blood to clot. The correct answer to the question is a) PT and aPTT (Activated Partial Thromboplastin Time), although INR is the more commonly used test in practice over aPTT for monitoring warfarin therapy. The PT and INR tests are essential for determining the correct dosage of Coumadin to balance the risk of clotting against the risk of bleeding.