Procalcitonin (PCT) is a 116 amino acid prohormone with a molecular weight of approximately 12.7 kD. PCT is expressed by neuroendocrine cells (C cells of the thyroid, pulmonary and pancreatic tissues) and successively enzymatically cleaved into (immature) calcitonin, katacalcin, and an N‑terminal region. The blood of healthy individuals contains only low levels of PCT. It was discovered that PCT increases during bacterial infection. It is probable that multiple tissues express PCT throughout the body in response to sepsis as was shown in an animal model. PCT circulating in septic patients consists of only 114 amino acids lacking the N - terminal dipeptide Ala‑Pro.
Increased PCT levels are often found in patients suffering from bacterial sepsis, especially severe sepsis and septic shock. PCT is considered as a prognostic marker to support outcome prediction in sepsis patients. In acute pancreatitis PCT was found to be a reliable indicator of severity and of major complications. In patients suffering from community - acquired respiratory tract infections or ventilator‑induced pneumonia PCT has been proposed as a guide for the decision of antibiotic treatment necessity and to monitor treatment success.