Final answer:
The effectiveness of warfarin sodium therapy is best measured using the International Normalized Ratio (INR), which calculates the blood's clotting time and helps in managing the anticoagulant therapy by keeping INR within a therapeutic range.
Step-by-step explanation:
The laboratory test best used to measure the effectiveness of warfarin sodium therapy is the International Normalized Ratio (INR). The INR is a calculation based on the results of a PT (prothrombin time) test that determines how long it takes your blood to clot. Warfarin, commonly referred to by the brand name Coumadin, is prescribed to prevent blood clots, and monitoring its effect is critical to ensure therapeutic efficacy while minimizing the risk of bleeding due to over-anticoagulation.
Management of warfarin therapy with the INR allows for standardized reporting, regardless of the test methods used by different labs. A higher INR value indicates a longer clotting time, and thus, a stronger anticoagulant effect of warfarin. Adjustments to the warfarin dose may be done based on INR results to maintain it within the therapeutic range, avoiding both excessive clotting and excessive bleeding.