"Your symptoms are data," Dr. Brooks tells her patients. "If a lab value comes back in the 'normal' reference range but you still feel unwell, that is not the end of the investigation. That's the beginning of a better question."

He mentions he's been tired. Not sick-tired — just tired in a way that didn't used to be there. Then he waves it off as getting older and changes the subject. Dr. Brooks hears this constantly, usually by accident, near the end of a visit for something else entirely.