Final answer:
The nurse should monitor the International Normalized Ratio (INR) to assess Coumadin toxicity, as an increased INR indicates delayed clotting. Blood Urea Nitrogen (BUN) and Bilirubin levels are important for assessing kidney and liver function, but not specific to Coumadin toxicity.
Step-by-step explanation:
The nurse should monitor the International Normalized Ratio (INR) to assess the client's Coumadin (warfarin) toxicity. The INR measures the speed of coagulation, comparing it to normal values. An increased INR indicates that it is taking longer for blood to clot, which can be a sign of Coumadin toxicity.
Other laboratory data that can be monitored include the Partial Thromboplastin Time (PTT), which assesses the intrinsic pathway of coagulation, but this is not the best answer choice as it is more commonly used to monitor heparin therapy.
Monitoring Blood Urea Nitrogen (BUN) levels and Bilirubin levels would be important for assessing kidney and liver function, respectively, but these are not specific to Coumadin toxicity.