Parathyroid Hormone (PTH)

Parathyroid hormone (PTH, synonyms: intact parathyroid hormone, iPTH; parathyrin) is a peptide hormone produced in the parathyroid glands (in the epithelial corpuscles/glandulae parathyroideae) via the precursors prepro-PTH and pro-PTH. Its half-life in the blood is very short, less than two minutes.It regulates calcium and phosphate balance. At the same time, it is involved in the biosynthesis of vitamin D.The regulation of PTH is mainly through ionized calcium. A decrease in the serum calcium level causes an increase in PTH. At the renal tubule, this leads to calcium reabsorption and inhibition of phosphate and bicarbonate reabsorption. At the bone, PTH stimulates osteoclasts (cells that break down bone substance) and thus bone resorption.The natural antagonist of parathyroid hormone is calcitonin.When blood levels of parathyroid hormone are decreased, the condition is called hypoparathyroidism; when blood levels are increased, the condition is called hyperparathyroidism.

The procedure

Material needed

  • Blood serum (1 ml), frozen.

Preparation of the patient

  • Blood collection is performed in the morning on an empty stomach

Interfering factors

  • Blood sample should be processed quickly (due torapid degradation by proteases); blood sample may need to be frozen (< 20 ºC).

Normal values

Normal value in pg/ml 10-65

Conversion factor

  • Pmol/l x 9.43 = pg/ml
  • Pg/ml x 0.106 = pmol/l

Indications

Interpretation

Interpretation of lowered values

  • Hypercalcemia (calcium excess; tumor-related) [Ca2+ ↑]
  • Hyperthyroidism (hyperthyroidism) [Ca2+ ↑]
  • Hypoparathyroidism (hypothyroidism) [Ca2+ ↓]
  • Milk-alkali syndrome (Burnett syndrome) – metabolic disorder in calcium balance caused by an excess of calcium carbonate or milk [Ca2+ ↑]
  • Sarcoidosis (synonyms: Boeck’s disease; Schaumann-Besnier’s disease) – systemic disease of connective tissue with granuloma formation [Ca2+ ↑]
  • Vitamin D overdose [Ca2+ ↑]

Interpretation of elevated values

  • Hyperparathyroidism, primary [Ca2+ ↑] and secondary [Ca2+ ↓] (parathyroid hyperfunction).
  • Parathyroid adenoma – benign tumor of the parathyroid gland.
  • Parathyroid hyperplasia – enlargement of the parathyroid gland, which is due to an increase in the number of cells.
  • Parathyroid carcinoma (parathyroid cancer).
  • Renal insufficiency (kidney weakness) [Ca2+ ↓]
  • Pseudo-hypoparathyroidism (PTH receptor defect; hypocalcemia (calcium deficiency) and hyperphosphatemia (phosphate excess)).
  • Osteomalacia – bone softening in adults.
  • Parathyroid formation (ectopic) of tumors (rare).
  • Rickets – bone softening in children.
  • Vitamin D deficiency [Ca2+ ↓]

Further notes

  • The marked increase in parathyroid hormone with declining renal function is mainly due to an increase in oxidized, inactive PTH. In contrast, the level of biologically active, nonoxidized PTH increases only moderately. Using cell cultures, researchers were able to demonstrate that only non-oxidized PTH, but not oxidized PTH, stimulates the synthesis of fibroblast growth factor 23 (FGF 23). Thus, only the non-oxidized PTH is part of the important hormonal regulatory circuit.Taking this into account, only PTH assays that measure only the bioactive PTH should be used in the future.