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. The INR (International Normalized Ratio) is the key test for monitoring warfarin therapy. The therapeutic range is typically 2.0-3.0 for most indications (e.g., DVT, atrial fibrillation). B. Fibrinogen levels do not assess warfarin effectiveness. C. aPTT monitors heparin therapy, not warfarin. D. Platelet count is important for clotting, but it does not measure warfarin effectiveness.