The nurse is caring for a client who is going home on warfarin. What laboratory test will the nurse inform the client will be used to evaluate therapeutic effects of the drug?

A. Activated partial thromboplastin time (APTT): APTT is primarily used to monitor heparin therapy, not warfarin. It measures the intrinsic and common pathways of the coagulation cascade but is not appropriate for evaluating warfarin's therapeutic effects. B. Platelet levels: Platelet levels are important for assessing clotting risk, but they do not directly reflect the effectiveness of warfarin. Warfarin works by inhibiting vitamin K-dependent clotting factors, which are best monitored by PT and INR. C. Prothrombin time (PT) and international normalized ratio (INR): Warfarin therapy is monitored using PT and INR. PT measures the time it takes for blood to clot, and INR standardizes this value across different laboratories. Maintaining the INR within a therapeutic range is key to preventing either clotting or bleeding complications. D. Prothrombin time (PT) and activated partial thromboplastin time (APTT): While PT is used to monitor warfarin, APTT is not relevant in this case. APTT is used for heparin therapy, not warfarin, so it is unnecessary for monitoring the effects of warfarin.