A client with arthritis has been receiving treatment with naproxen and now reports ongoing stomach pain, increasing weakness, and fatigue. Which laboratory test should the nurse monitor?

A. Osmolality: Osmolality measures the concentration of solutes in the blood and is not typically affected by naproxen or indicative of the reported symptoms. B. Serum calcium: While naproxen can cause gastrointestinal irritation and ulceration, it does not typically affect serum calcium levels. Monitoring serum calcium would not directly address the client's reported symptoms. C. Erythrocyte sedimentation rate (ESR): ESR is a nonspecific marker of inflammation and is not directly related to the reported symptoms of stomach pain, weakness, and fatigue associated with naproxen use. D. Hemoglobin: Naproxen, a nonsteroidal anti-inflammatory drug (NSAID), can cause gastrointestinal bleeding, which may lead to anemia and a decrease in hemoglobin levels. Monitoring hemoglobin levels can help assess for gastrointestinal bleeding in this client who is experiencing stomach pain and weakness/fatigue.