PTH

Parathyroid hormone (PTH), an 84 amino acid polypeptide, plays a critical role in the regulation of mineral homeostasis and bone metabolism [1].  The measurement of PTH is used in conjunction with calcium determinations to assess disorders in calcium metabolism [2-4].  PTH affects mineral homeostasis by regulating the rate of kidney mediated reabsorption of calcium and phosphorus and by stimulating the synthesis of calcitriol in the kidney.  The direct effect of PTH on bone is to stimulate osteoclastic bone resorption, which is coupled with an increase in bone formation.  PTH is an important regulator of calcium homeostasis.

The measurement of PTH has proven to be difficult due to the heterogeneity of peptides that occur in both the gland and circulation [5].  In addition to the formation of fragments within the gland, there is further proteolytic breakdown of PTH once it is released into the circulation [6,7]. Parathyroid hormone and its fragments are cleared from the circulation by both the kidneys and liver [8].  The clearance of C-terminal fragments is slower than the clearance of the intact hormone and is more dependent upon renal mechanisms [9].

Primary and secondary hyperparathyroidism, kidney insufficiency, malabsorption-syndrome and pseudo-hypoparathyroidism result in elevated concentrations of PTH [10]. Decreased concentrations of PTH coincide with high doses of vitamin-D fortified milk, milk-alkali-syndrome, Morbus Boeck (sarcoidosis), hyperthyreosis, ingestion of thiazide and hypercalcemia of malignancy.  

PTH concentration is also decreased with absorptive hypercalciuria and hypoparathyroidism.

  1. Blumsohn A. Al Hadan A 2002 Parathyroid Hormone: What Are We Measuring and Does It Matter? Annals of Clinical Biochemistry 39. pp. 169 – 172. 
  2. Pribor HC, Fabisinski LF 1983 Artificial Intelligence in Laboratory Medicine III: The Parathyroid Hormone Profile MLO.
  3. Habener JF, Segre GV 1979 Parathyroid Hormone Radioimmunoassay, Annals of Internal Medicine 91, 782.
  4. Kao Pc, Jiang N et al 1982 Development and Validation of a New Radioimmunoassay for Parathyrin (PTH), Clinical Chemistry 28, 69.
  5. Lindall AW, Wong ET 1975 Column Chromatography of Human Serum Parathyroid Immunoreactive Peptides, Proceedings of the Society for Experimental biology and Medicine 148, 799.
  6. Segre GV, Habener JF et al 1972 Parathyroid Hormone in Human Plasma, Journal of Clinical Investigation, 51, 3163.
  7. Martin KJ, Hruska KA et al 1979 The Peripheral Metabolism of Parathyroid Hormone, NEJM 301, 11092.
  8. Potts JT, Habener JF 1990 Fundamental Considerations in the Physiology, Biology and Biochemistry of Parathyroid Hormone. In: Metabolic Bone Disease and Clinically Related Disorders, Avioloi and Krane, eds. W.B. Saunders, Second Edition, 69.
  9. Freitag J, Martin Kj et al 1978 Impaired Parathyroid Hormone Metabolism in Patients with Chronic Renal Failure, NEJM 298, 29.
  10. Segre GV, Niall HD, Habener JF, Potts Jr, JT 1974 Metabolism of Parathyroid Hormone: Physiologic and Clinical Significance Am J Med 56(6), 774 - 784.