PTH and hyperparathyroidism: Postoperative hyperparathyroidism is not an uncommon finding after parathyroidectomy for classical PHPT, with a mean prevalence of 23.5% among various studies, mostly related to vitamin D deficiency or insufficiency or lack of Ca through diet or supplements.(58) As opposed to PHPT where this finding invariably represents a form of secondary hyperparathyroidism because the Ca normalizes, elevated PTH levels found after surgery for NHPT may be the only sign of disease persistence, possibly hinting at a previously unidentified cause of secondary hyperparathyroidism involving multiple glands.