Intact PTH (Паратиреоидный гормон)

The Intact Parathyroid Hormone (PTH) test, also known as parathormone or parathyrin, assesses parathyroid gland function and the regulation of calcium–phosphate homeostasis. When interpreted alongside serum or ionized calcium, intact PTH helps categorize disturbances of calcium balance. It supports differentiation of primary, secondary, and tertiary hyperparathyroidism; establishes the diagnosis of hypoparathyroidism; and provides longitudinal assessment in chronic disorders of calcium metabolism. The assay is also used to evaluate response to therapy and for postoperative surveillance after parathyroidectomy performed for parathyroid neoplasms.

Parathyroid hormone is produced by the parathyroid glands located on the posterior aspect of the thyroid lobes. The intact hormone is an 84–amino acid peptide with a short circulating half-life of approximately four minutes. N‑terminal and C‑terminal fragments persist longer in circulation and differ in activity and metabolism from the intact molecule. PTH maintains stable extracellular calcium and phosphate concentrations through tightly regulated secretion. Release of PTH varies inversely with serum ionized calcium via negative feedback and is influenced by vitamin D status, phosphorus, and magnesium. Secretion rises during hypocalcemia and is suppressed when calcium is elevated. PTH actions include stimulation of osteoclastic bone resorption, enhancement of renal tubular calcium reabsorption, inhibition of renal phosphate reabsorption, and promotion of intestinal calcium absorption. Calcitonin, secreted by thyroid C cells, acts as a physiologic antagonist, and PTH production declines once normocalcemia is restored. Excess PTH production (hyperparathyroidism) produces hypercalcemia, hyperphosphaturia, generalized osteoporosis, vascular calcification, and gastrointestinal mucosal involvement. PTH deficiency (hypoparathyroidism) leads to hypocalcemia with hyperphosphatemia and may result in seizures and tetany. Accurate interpretation requires concurrent measurement of ionized (free) calcium and correlation with clinical findings and other laboratory and imaging studies to distinguish overlapping disorders and guide management.