PTH and vitamin D deficiency: Extensive or repeated neck operations, Graves’ disease history, total thyroidectomy, bilateral neck exploration for PHPT, failure to identify >2 parathyroid glands during surgery or presence of parathyroid glands in the specimens, postoperative complications, younger age, vitamin D deficiency, a lower preoperative and a lower postoperative corrected calcium, as well as a larger decline in postoperative calcium and PTH are well recognized risk factors for PH (421, 433).