CALCA and Immunodeficiency: Recent studies have indicated that, as an inactive propeptide substance of calcitonin and an indicator for systemic inflammatory reaction, PCT has a high specificity and sensitivity and is superior to other inflammatory factors in the diagnosis of bacterial infection, and its concentration is not susceptible to immunodeficiency conditions and use of corticosteroids; its diagnostic value has been significantly superior to CRP and other cytokines11–15.