A nurse is preparing to administer warfarin to a client who has chronic atrial fibrillation. Which of the following laboratory values should the nurse monitor prior to administering the medication?

A. LDL: Low-density lipoprotein (LDL) is used to assess cholesterol levels and cardiovascular risk, but it does not influence warfarin therapy. Monitoring LDL is not relevant to dosing or safety of anticoagulation. B. BUN: Blood urea nitrogen (BUN) reflects kidney function, which is important for some medications, but warfarin is metabolized by the liver, not the kidneys. BUN is not required before administering warfarin. C. INR: The international normalized ratio (INR) measures the effectiveness of warfarin and the client’s coagulation status. Monitoring INR ensures the dose is therapeutic and reduces the risk of bleeding or clot formation in atrial fibrillation. D. Hct: Hematocrit measures the proportion of red blood cells and helps assess anemia or blood loss, but it does not guide warfarin dosing. While low Hct may indicate bleeding, INR is the primary laboratory value to monitor before administration.