PCT is a precursor of the hormone calcitonin and is synthesized physiologically by thyroid C cells. PCT levels are low in homeostatic conditions. In bacterial infections, PCT is synthesized in various extrathyroidal neuroendocrine tissues. Overall, PCT secretion is a component of the inflammatory response that appears to be relatively specific to systemic bacterial infections.
PCT is a 116-amino acid polypeptide precursor to the calcium regulatory hormone calcitonin. It is composed of three sections (see image on the right):
- The amino terminus (N-ProCT)
- Immature calcitonin
Synthesis of PCT is regulated by the Calc-1 gene located on chromosome 11. In healthy individuals, production of PCT, and subsequently calcitonin, is restricted to the thyroid C cells.