Abstract:Serum procalcitonin (PCT) is propeptide of calcitonin, normally produced by thyroid C cells. And C-reactive protein (CRP) is a sort of acute phase protein secreted by hepatic cells in the induction of IL-6. Substantial studies have shown that the serum levels of PCT and CRP are increased remarkably in the patients who suffered from infectious diseases, and the levels are positively correlated with the severity of the infectious disorders. There is no apparent difference in the sensitivity of diagnosing infectious diseases between the 2 proteins, but the specificity of PCT is higher than that of CRP. It is of great clinical application value and promising application prospect when the 2 proteins are combined together in the differential diagnosis of infection and noninfectious diseases, the monitoring of critical illness and severe infection, the guiding of appropriate antibiotics usage, and the evaluation of curative effects and prognosis. However, how the PCT is produced and through what mechanism it exerts effect remain unclear and need further studies.