Causes of high calcitonin include bacterial, fungal and parasitic infections, etc. Severe infections can lead to multi-organ dysfunction and even severe shock. Calcitonin is composed of proteins and is mainly secreted by thyroid C-cells. Its concentration in the body is very low, and it is only when the patient is infected by microorganisms, such as bacteria, that it is released into the bloodstream, leading to an increase in blood calcitonin concentration. Blood calcitoninogen concentration varies with the severity of bacterial infection. Extremely elevated blood calcitoninogen concentration often reflects severe infection, which can lead to systemic inflammatory response syndrome, multi-organ dysfunction, and even infectious shock. If you find discomfort or abnormal test results, consult a doctor as soon as possible to avoid delaying your condition.