Procalcitonin
Procalcitonin is the precursor of calcitonin, a calcium regulatory hormone, which is also an acute phase reactant that increases in response to systemic inflammation since it is thought to represent the activation of innate immunity in response to invasion by bacteria, malaria, and some fungi (not viruses). It was originally believed that procalcitonin levels increased in response to tissue injury or sepsis induced only by infection; however, levels of procalcitonin may be elevated in other inflammatory diseases or situations such as autoimmune diseases, severe trauma, cirrhosis, pancreatitis, and hypotension during surgery.

Current research suggests that the level of procalcitonin elevation may provide useful diagnostic information, with levels >=10 mcg/mL indicative of sepsis/systemic bacterial infection, levels between 2 and 10 mcg/mL suggestive of sepsis, and levels between 0.25 and 2 mcg/mL suggestive of other conditions or localized infection.

In addition, the procalcitonin level may be useful for assessing the efficacy of empiric antibiotic therapy as well as for determining when antibiotic therapy can be discontinued during the treatment of an infection. However, further research is needed to define the exact role of procalcitonin in the diagnosis and management of infections.