Bone metabolism is significantly influenced by the activity of osteoblasts and osteoclasts, the calciotropic hormones 1,25-dihydroxy vitamin D, parathyroid hormone and calcitonin, as well as the extracellular calcium concentration.
Parathyroid hormone (PTH) is a peptide hormone which is synthesised in the parathyroid glands. The main function of PTH is to increase the concentration of calcium in the blood plasma. Intact PTH (iPTH) is the biologically active form and is secreted when the calcium level is low. iPTH is eliminated from the circulation after a half-life of less than four minutes.
The quantification of iPTH is important for the diagnosis of primary hyperparathyroidism due to solitary parathyroid adenoma with atrophy of the other parathyroid glands or primary hyperplasia of all four parathyroid glands. The uncontrolled increase of PTH level with resulting hypercalcaemia leads to changes in the bone with decrease of bone mass and nephrolithiasis (calcium oxalate or calcium phosphate-containing kidney stones). In over 90% of patients with primary hyperparathyroidism, increased iPTH concentrations are observed.
Moreover, the combined determination of 25-OH vitamin D, iPTH and calcitonin levels may provide information on whether or not bone metabolism disorders or diseases are present.