The nurse is reviewing the client's laboratory values. Which serum laboratory value indicates to the nurse that a prescription for atorvastatin is having the desired effect for a client at risk for coronary artery disease?

A. High density lipoprotein (HDL): HDL levels are important for cardiovascular health as higher levels are associated with a lower risk of coronary artery disease. However, atorvastatin primarily targets LDL levels. While increasing HDL is beneficial, it is not the primary measure of atorvastatin's effectiveness. B. Low density lipoprotein (LDL): Atorvastatin is a statin medication used to lower LDL cholesterol levels, which is a major risk factor for coronary artery disease. A decrease in LDL levels indicates that the medication is having its desired effect, reducing the risk of cardiovascular events. C. Creatine phosphokinase (CK): CK levels are monitored to assess muscle damage or side effects related to statin use, such as rhabdomyolysis. While important for safety monitoring, changes in CK levels do not directly reflect the effectiveness of atorvastatin in managing cholesterol levels. D. Prothrombin time (PT): PT is used to evaluate blood clotting ability and is not directly related to the effectiveness of atorvastatin. It is more relevant for monitoring anticoagulant therapy rather than statin therapy for cholesterol management.