This young woman presents with some classic features of anorexia/bulimia, i.e., a history of nausea and vomiting, markedly low body weight for height, and tooth erosions. Her electrolyte values are consistent with her history of nausea and vomiting. Most comprehensive biochemical panels do not routinely include serum phosphate determination, and it is likely that her phosphate concentration upon admission would have been within reference ranges. However, treatment with dextrose should stimulate insulin secretion, driving phosphate into the cells. In a normally nourished individual, the drop in serum phosphate would be mild and would result in no symptoms. However, in a chronically malnourished patient, the drop can be profound and can lead to delirium, heart failure, and rhabdomyolysis, i.e., the acute hypophosphatemic syndrome. She had a borderline hyponatremia upon admission, but treatment with isotonic sodium chloride solution would be expected to increase, not decrease, her serum sodium level. Thus, her osmolality would increase. The absence of fever, nuchal rigidity, or any neurologic signs or symptoms upon admission make the diagnosis of viral meningitis less likely. Alcohol withdrawal can also manifest as acute confusion, but it is not commonly observed in persons of this age group and this patient has no history of alcohol abuse. Acute hypokalemia generally does not produce confusion.