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 is important for assessing clotting, but INR is more relevant for monitoring warfarin therapy. B. Fibrinogen levels are not the primary measure for warfarin management. C. The INR (International Normalized Ratio) is the key test used to adjust warfarin dosing, as it measures the clotting tendency. D. aPTT is useful for monitoring heparin therapy, not warfarin.