Hyperparathyroidism is overactivity of the parathyroid glands resulting in excess production of parathyroid hormone (PTH). Increased PTH consequently leads to increased serum calcium (hypercalcemia) due to 1) increased bone resorption, allowing flow of calcium from bone to blood, 2) reduces renal clearance of calcium, and 3) increases intestinal calcium absorption. Etiology Primary hyperparathyroidism results from a dysfunction in the parathyroid glands themselves, with oversecretion o ...