Procalcitonin (PCT) is the prohormone of Calcitonin. It is also released by monocytes and macrophages rapidly in response to bacterial infections. Unlike the typically used biomarkers of inflammation (CRP and ESR), it does not rise in malignancies (or non-infectious inflammatory conditions with the following exceptions: medullary thyroid cancer, small cell lung cancer, administration of OKT3 and ATG, in the first 24 hours after trauma or surgery, in the first 48 hours of life, Adult Onset Still's Disease (AOSD), Wegener's granulomatosis and Kawasaki's Disease. As a clinical lab test PCT has been found to be useful in the following settings: 1) Antimicrobial Stewardship - numerous studies have shown that ability to use PCT as part of clinical decision making in stopping antibiotic therapy. In these studies antibiotic use mas discouraged if the PCT was < 0.5ng/ml and strongly discouraged if the PCT was < 0.25ng/ml. An important caveat is that a single PCT measu