Parathyroid hormone (PTH) is a hormone secreted by the parathyroid glands with important functions in the kidney, intestine and bone. These include calcium absorption and regulation, phosphate regulation, bone remodeling, osteoclast activation, and conversion of vitamin D to its active form, calcitriol, in the kidneys. In immunohistochemistry, PTH antibodies may be used to identify parathyroid tissue, where they show strong cytoplasmic staining in chief cells. Staining intensity has been found to decrease in hyperplastic tissue and adenomas when compared to normal parathyroid tissue. References: Archives of Pathology & Laboratory Medicine. 2010 Nov. 134 (11), 1639-1644, PMID: 21043817; Southern Medical Journal. 2004 May. 97 (5): 506–11, PMID: 15180028; Mol Cell Endocrinol. 2011 Dec 5;347(1-2):25-9, PMID: 21664413; Bone Res. 2016 Oct 18;4:16041, PMID: 27790378; J Endocrinol Invest. 2011 Jul;34(7 Suppl):18-22, PMID: 21985975