A 19-year-old college student is brought to the emergency department by campus police after being found in the library talking to himself, rearranging books according to a system he says was communicated to him telepathically, and expressing the belief that his professors are part of a surveillance network. He has no prior psychiatric history. His parents report a two-month decline in functioning with social withdrawal and deteriorating academic performance. Physical examination reveals a thin male with mild tachycardia but is otherwise unremarkable. Which laboratory assessment approach is most appropriate for the initial evaluation of this patient presenting with new-onset psychosis?