Procalcitonin is a precursor molecule of calcitonin which is a peptide hormone. C cells of the thyroid and lung endocrine cells mainly produce precalcitonin. Procalcitonin consists of 116 amino acids and has 13 k Da molecular weight. The prohormone calcitonin was first discovered which was cleaved intracellularly into active hormone by proteolytic enzymes. The procalcitonin levels are below detection limit in healthy subjects. Elevated levels of procalcitonin is observed in patients with bacterial infections. Bacterial endotoxins and inflammatory cytokines induce production of procalcitonin. The neuroendocrine cells in the lungs and intestine are usually responsible for production of procalcitonin during inflammation. Procalcitonin role in phosphate and calcium metabolism during sepsis are still unclear.

Levels of circulating procalcitonin are elevated only in cases of medullar carcinomas in thyroid or small cell lung carcinoma. Procalcitonin has become an important protein for detection of inflammation after its report in patient with bacterial infection. None of the enzymes are known which can break down the circulating procalcitonin. CALC-I is the gene localized in chromosome 11 in humans forms the calcitonin precursor. Procalcitonin has been studied for its role in metabolism of calcium, pain relieving effects, and cytokine network and modulation of NO synthesis. The structural similarities of calcitonin and procalcitonin is what makes it a hypothetical candidate for a role in calcium and phosphate metabolism in sepsis. Sepsis and bacterial infections lead to highest plasma levels of procalcitonin. The type and extent of inflammation affects the level of procalcitonin. Procalcitonin levels are not elevated during autoimmune inflammation or viral infections. Medullar carcinomas and renal failures lead to increased levels of procalcitonin. Around 1000ug/ml concentrations of procalcitonin is detected during severe bacterial infections whereas in healthy subjects and under normal conditions the concentration of procalcitonin in plasma or serum does not exceed 0.5 ug/ml.