Serum 25(OH)D will be measured by ARUP Laboratories (Salt Lake City, UT, USA) using a chemiluminescent immunoassay. Serum calcium and phosphorus will be determined by The Methodist Hospital Clinical Chemistry Department as part of the standard bariatric protocol comprehensive metabolic panel. Intact PTH (iPTH) assays will be performed using the ADVIA Centaur ® XP Immunoassay System.