A mother brings her adult son to your office, relating a history of two weeks of difficulty sleeping, irritability, and problems with relationships with others. He has also been very talkative, expressed a multitude of "great ideas" and just seems to "talk constantly." Several weeks ago, he seemed depressed. Which of the following diagnostic studies would be the most helpful in his evaluation?
A. complete blood count
B. random blood sugar
C. free T4 level
D. liver function studies
E. head CT scan