An older man with osteoarthritis presents for a routine medication check. The Nurse Practitioner educates the patient on longterm use of NSAIDS. What diagnostic or laboratory test should the NP order?

A. Serum creatinine: Long-term NSAID use can impair renal perfusion by inhibiting prostaglandin-mediated vasodilation of the afferent arteriole, potentially leading to acute kidney injury or chronic kidney disease. Monitoring serum creatinine allows early detection of nephrotoxicity and adjustment of therapy. B. Serum glucose: NSAIDs do not directly affect glucose metabolism or insulin function. Routine glucose monitoring is not indicated solely for NSAID therapy unless the patient has comorbid diabetes. C. Serum arachidonic acid: Measurement of arachidonic acid levels is not used in routine clinical practice to monitor NSAID safety or efficacy. NSAID effects are monitored through organ function and symptom control rather than biochemical substrate levels. D. Lower extremity ultrasound: Ultrasound is not indicated for monitoring NSAID-related adverse effects. Imaging of extremities is used for structural or vascular assessment, which is unrelated to routine NSAID safety surveillance.