Procalcitonin (PCT) is a precursor to the thyroid hormone calcitonin. It is normally produced by special cells in the thyroid gland called C-cells and is present in low levels in the blood. It may also be made by other cells in the body when stimulated by an intense stressor, in particular systemic bacterial infection (sepsis). Other stressors include infection from other causes, tissue damage due to events such as trauma, surgery, pancreatitis, burns, cardiogenic shock – related to a heart attack – and acute organ transplant rejection. Procalcitonin has been identified as a promising biomarker that may assist in distinguishing bacterial infection from other causes of fever or sepsis (e.g., viral infections) that do not lead to an increase in serum PCT levels.  The level of PCT in the serum is reportedly a reflection of the severity of bacterial infection, ranging from slightly elevated in infections with minor systemic inflammatory response to very high values in cases of severe sepsis and septic shock.  Once an infection is under control, PCT levels decrease. It is a more specific test and provides more information about the severity and the course of the disease than that of CRP (C-Reactive Protein). This gives the procalcitonin test the potential to be used to help detect the presence of a severe bacterial infection in its early stages. Also, this test may be ordered at intervals to monitor the effectiveness of antimicrobial treatment.