Procalcitonin (PCT)

Procalcitonin is a **116-amino-acid prohormone peptide** with a molecular weight of approximately 13 kDa, encoded by the **CALCA gene**. In healthy individuals, it is produced by thyroid C cells and is rapidly cleaved to the hormone calcitonin, involved in calcium homeostasis. During systemic bacterial infections and severe inflammatory responses, procalcitonin is produced extra-thyroidally (notably by neuroendocrine cells in organs such as lung and intestine) and released into the bloodstream in much greater quantities. **Procalcitonin does not have a known physiological receptor or direct biological activity**; its primary clinical significance is as a **highly specific and sensitive biomarker for bacterial infection and sepsis**, helping to distinguish bacterial from viral infections and to optimize antibiotic stewardship. Elevated PCT levels are of high negative predictive value for excluding bacterial causes in infectious and inflammatory states. It is not itself a therapeutic target, but it has a critical role in guiding clinical decision-making, especially for initiation and discontinuation of antibiotic treatment in conditions like sepsis, lower respiratory tract infections, and other acute inflammatory states.

Other names

Calcitonin precursor polyproteinCalcitonin, proPro-CalcitoninCalcitonin 1Calcitonin related polypeptide alpha