A nurse is caring for a client who is receiving warfarin 5 mg PO daily. Which of the following laboratory values should the nurse check prior to administering the medication? (Select all that apply.)

A. BUN: Blood urea nitrogen is a marker of renal function and is not directly affected by warfarin therapy. While renal function is important for overall medication safety, it does not guide warfarin dosing or anticoagulation monitoring. B. Serum potassium: Potassium levels are important for cardiac and neuromuscular function but are not influenced by warfarin. Monitoring potassium is unrelated to evaluating the effectiveness or safety of warfarin therapy. C. PT: Prothrombin time measures the extrinsic and common coagulation pathways, which are directly affected by warfarin. Checking PT before administration helps assess anticoagulation status and the risk of bleeding, allowing for appropriate dose adjustments. D. Serum sodium: Sodium levels are critical for fluid balance and neurologic function but do not affect warfarin therapy or coagulation. Monitoring sodium is not necessary for safe administration of warfarin. E. INR: International normalized ratio standardizes PT results to guide warfarin therapy safely. It provides a reliable measure of anticoagulation and bleeding risk, and checking INR before administering warfarin ensures the dose is appropriate for therapeutic anticoagulation.