Hypoparathyroidism is characterised by hypocalcaemia, hyperphosphataemia and low or inappropriately normal levels of parathyroid hormone (PTH). Pseudohypoparathyroidism is characterised by similar findings but PTH is elevated due to PTH resistance.
PTH is a key calcium-regulating hormone essential for calcium homeostasis, vitamin D-dependent calcium absorption, renal calcium reabsorption and renal phosphate clearance.
PTH is secreted by the four parathyroid glands, located in the neck behind the thyroid gland. It regulates serum calcium and phosphorus levels and also plays a part in bone metabolism. Low levels of PTH cause serum calcium levels to fall and serum phosphate levels to rise.