A 75-year-old male has been diagnosed with prostate cancer. …

A 75-yeаr-оld mаle hаs been diagnоsed with prоstate cancer.  Prior to starting radiation therapy, the physician sent the client for bloodwork as they were concerned that the cancer may have metastasized to the client's skeletal system. Which one of the following laboratory analytes would provide this information to the nurse when the results return?