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 measures the concentration of solutes in the blood and is not typically affected by naproxen or indicative of the reported symptoms. B: 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: 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: 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.