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?

A. Platelet count: Platelet count evaluates clotting potential related to platelet number, but it is not used to monitor or dose warfarin therapy. Warfarin affects vitamin K–dependent clotting factors rather than platelets. B. Fibrinogen level: Fibrinogen is a plasma protein essential for clot formation, but it is not used to guide warfarin therapy. Fibrinogen testing is more relevant in bleeding disorders or DIC, not routine anticoagulation management. C. aPTT: Activated partial thromboplastin time (aPTT) is primarily used to monitor heparin therapy. Warfarin does not significantly alter aPTT, so this test is not appropriate for warfarin dose adjustments. D. INR: The international normalized ratio (INR) standardizes prothrombin time and is the primary laboratory test used to monitor warfarin therapy. Reporting the INR allows the provider to safely adjust the daily warfarin dose to maintain therapeutic anticoagulation.