A nurse is reporting a client's laboratory tests to the provider to obtain a prescription for the client's daily warfarin. Which of the following laboratory tests should the nurse plan to report to obtain the prescription for the warfarin?

Rationale: A. Fibrinogen level: Fibrinogen is a clotting factor that can reflect coagulation activity, but it is not used to monitor warfarin therapy. It is more relevant in conditions like DIC or liver disease, not for warfarin dose adjustments. B. aPTT: Activated partial thromboplastin time (aPTT) is used to monitor heparin therapy. Warfarin, which affects the extrinsic pathway of coagulation, does not significantly impact aPTT levels. C. INR: The international normalized ratio (INR) is the standard test used to monitor warfarin therapy. It reflects the effect of warfarin on prothrombin time and guides safe and effective dosing to maintain therapeutic anticoagulation. D. Platelet count: While platelet count helps evaluate bleeding risk and detect thrombocytopenia, it is not used to guide warfarin dosing. Warfarin works by inhibiting vitamin K–dependent clotting factors, not by affecting platelet production.