In the absence of infection, the extra-thyroidal expression of the PCT gene in the liver, lung, kidney, adrenal tissue, monocytes, granulocytes, testis, prostate gland, and small intestine is suppressed.7 Procalcitonin in the blood of healthy individuals is below the limit of detection of clinical assays, but microbial infection, especially of bacterial origin, induces a ubiquitous increase in PCT gene expression, resulting in the constitutive release of PCT from parenchymal tissues throughout the body. This evidence concerns the gene CALCA and infection.