In caring for a client who is receiving linezolid IV for nosocomial pneumonia, which assessment finding is most important for the nurse to report to the health care provider?

Choice A: Yellow-tinged sputum is not a serious adverse effect of linezolid. It may indicate an infection or inflammation in the respiratory tract, but it does not require immediate attention from the health care provider.

Choice B: Nausea and headache are common side effects of linezolid. They are usually mild and self-limiting, and they can be managed with supportive measures such as hydration, rest, and analgesics.

Choice C: Watery diarrhea is a sign of pseudomembranous colitis, a potentially life-threatening complication of linezolid. It is caused by an overgrowth of Clostridium difficile bacteria in the colon, which produce toxins that damage the intestinal mucosa. It can lead to dehydration, electrolyte imbalance, sepsis, and perforation. The nurse should report this finding to the health care provider immediately and stop the linezolid infusion.

Choice D: Increased fatigue is not a specific or serious adverse effect of linezolid. It may be related to the underlying infection, anemia, or other factors. It does not require urgent intervention from the health care provider.

Choice A: Creatinine is not a relevant laboratory test for the nurse to monitor, as this reflects renal function and is not affected by naproxen or arthritis. This is a distractor choice.

Choice B: Serum calcium is not a pertinent laboratory test for the nurse to monitor, as this indicates bone metabolism and is not related to naproxen or arthritis. This is another distractor choice.

Choice C: Erythrocyte sedimentation rate is not an important laboratory test for the nurse to monitor, as this measures inflammation and is not influenced by naproxen or stomach pain. This is another distractor choice.

Choice D: Hemoglobin is an essential laboratory test for the nurse to monitor, as this shows blood oxygen-carrying capacity and can be reduced by naproxen-induced gastrointestinal bleeding, which can cause stomach pain, weakness, and fatigue. Therefore, this is the correct choice.