Q. A 45-year-old man comes to his primary care physician complaining of low back pain. Pt. has a history of athletic competition and believes this is arthritic, but describes the pain as “something more than usual.” The patient indicates a recent history of polyuria, polydipsia, hypertension, and weight gain. X-ray of the spine shows an L4-L5 compression fracture. Which of the following is most likely to be elevated in this patient?