A patient who has been well-managed on lithium carbonate for…

A patient who has been well-managed on lithium carbonate for bipolar disorder is admitted to the emergency department with confusion, coarse hand tremors, and ataxia. The patient’s spouse reports that the patient recently had a severe stomach flu with prolonged vomiting and diarrhea. Which laboratory abnormality should the nurse anticipate as the primary cause of the patient’s current symptoms?