A 40-year-old woman with bipolar disorder presents to the em…
A 40-year-old woman with bipolar disorder presents to the emergency room 2 weeks after starting a new medication. She reports that she was doing well until she got a viral gastroenteritis and was unable to eat for several days. While the viral symptoms have resolved, she now complains of nausea and vomiting, ataxia and tremor. Which of the following studies should be ordered first?