Hyperparathyroidism

Parathyroid hormone (PTH) is released when the body senses low circulating calcium. It raises serum calcium by increasing calcium release from bone, increasing renal calcium reabsorption, and supporting activation of vitamin D, which increases intestinal calcium absorption. PTH also promotes phosphate excretion by the kidneys, so phosphate is often low when PTH is excessive. Hyperparathyroidism means PTH secretion is excessive for the patient’s physiologic state. The type matters because the calcium pattern reveals whether the parathyroid glands are the problem or are responding appropriately to another problem. - Primary hyperparathyroidism is autonomous PTH secretion, usually from one overactive gland. The result is hypercalcaemia with a PTH concentration that is elevated or remains within the reference range when it should be suppressed. - Secondary hyperparathyroidism is a compensatory response to chronic hypocalcaemic stimuli, such as chronic kidney disease, vitamin D deficiency, or malabsorption. PTH is high, but calcium is usually low or normal. - Tertiary hyperparathyroidism develops after longstanding secondary stimulation, most often with advanced kidney disease. The glands become autonomous, producing high PTH despite hypercalcaemia. The defining clinical mismatch in...