Calcitoninogen is a blood biochemical test and should be drawn from a yellow tube and assayed with serum. Calcitoninogen is a glycoprotein with a molecular weight of 13KDa, which is produced by thyroid C cells under normal physiological conditions, so it is also known as thyrocalcitonin; Calcitoninogen has no hormonal activity, and its detection process is virtually free from external interference, with high sensitivity and specificity, and is widely used in the diagnosis of infections. Calcitonin is an acute time-phase reactive protein, and its level can reflect the degree of activity of infectious diseases; viral infections and non-specific inflammation do not lead to an increase in the level of calcitonin; however, bacterial infections, severe shock, and multiple organ failure syndromes can lead to a significant increase in the level of calcitonin, and the magnitude of the increase is closely related to the severity of the disease and the prognosis of the patient. Calcitoninogen test is often used to identify infectious diseases. Normally, elevated calcitoninogen suggests bacterial infection, while normal calcitoninogen can exclude the possibility of bacterial infection, and calcitoninogen test should be performed under the guidance of a physician.