PCT is the acronym for procalcitonin, a sensitive indicator of systemic inflammation. When the body has obvious serious infections, especially various bacterial infections, fungal infections, parasitic infections, the concentration of PCT is obviously increased, PCT is also seen in the whole body for all kinds of inflammation over-expression of immunity, clinically known as overreaction syndrome. However, when the body has mild inflammation, limited inflammation, chronic inflammation, the concentration of PCT is generally not significantly increased, because of this, PCT can be used as a sensitive indicator of clinical inflammation and the severity of the inflammatory response. The higher the PCT indicates that the body’s inflammatory response is more serious, often also represents the more serious condition, when the condition is under control, the concentration of PCT will also be significantly reduced.