Procalcitonin is a precursor of the peptide hormone calcitonin. Procalcitonin is mainly produced by the neuroendocrine cells of the lung and thyroid gland, but may be secreted ubiquitously during inflammation or infection. Under normal expression conditions, procalcitonin is immediately cleaved into three specific fragments: calcitonin, katacalcin, and an N terminal residue. Levels of unprocessed procalcitonin are significantly increased after bacterial infection, inflammation, trauma, or shock.