Calcitonin CT test, clinically referred to as PCT, is a blood-based indicator for detecting infection in the patient’s organism and is a diagnostic indicator of infection with a high specificity and a good predictor of whether the infection is under control or not. PTC is a sensitive early indicator for the diagnosis of infectious diseases because it is usually undetectable due to the low level of calcitonin in normal human body, but after the occurrence of infection, the PTC value will increase in 2-3 hours after infection and reach the peak in 6 hours. A sensitive indicator to differentiate bacterial infection from non-bacterial infection. In clinical practice, PTC, temperature, and C-reactive protein are usually analyzed together to determine whether a patient has an infectious disease and the severity of the infection, and to provide some guidance for treatment.