PTH and hyperthyroidism: Hypoparathyroidism is characterized by low parathyroid, low calcium, and high phosphate serum levels. Primary (idiopathic) hypoparathyroidism results from failure of the parathyroid gland to secrete parathyroid hormone. Secondary hypoparathyroidism (characterized by a low or absent parathyroid level) has numerous causes: neck surgery (for cancer, goiter, nodules, hyperthyroidism), radiation therapy to the neck, magnesium depletion, autoimmune diseases, and inherited conditions. The appearance of affected individuals is normal.