The nurse should emphasize the importance of point C: Report vomiting or diarrhea. This is because lithium can cause toxicity if the levels in the body become too high. Vomiting or diarrhea can lead to dehydration, which can increase the concentration of lithium in the blood to potentially toxic levels. Therefore, it is crucial for the client to report vomiting or diarrhea promptly so that appropriate measures can be taken to manage their lithium levels.
