Among several markers of inflammation and sepsis, procalcitonin (PCT) markers is being studied to investigate their accuracy for the diagnosis of bacterial infections. PCT is the prehormone of calcitonin, which is normally secreted by the C cells of the thyroid in response to hypercalcemia; under these normal conditions, negligible serumPCT concentrations are detected. The mechanism proposed for PCT production after inflammation and its role are still not completely known. It is believed that PCT is produced by the liver and peripheral blood mononuclear cells, modulated by lipopolysaccharides and sepsis-related cytokines. It binds to polysaccharides in pathogens, activating the classical complement pathway. The reported diagnostic accuracy of PCT for the diagnosis of bacterial infections has varied across studies.