Compared with C-reactive protein (CRP) and various inflammatory response factors (bacterial endotoxin, TNF-α, IL-2), procalcitonin (PCT) is diagnosed and differentiated in systemic bacterial infections, therapeutic effects and prognosis The aspect is more effective. Sensitive and clinically more useful. 1. PCT is more sensitive and specific than other inflammatory response factors. PCT has more than 95% sensitivity and specificity in bacterial infections, especially sepsis, especially severe sepsis and sepsis. The diagnostic specificity of septic shock is as high as 100%. PCT is the earliest in plasma. Plasma concentrations in patients with systemic bacterial infections are earlier than CRP and other inflammatory factors. It can be detected within 2 hours and 6 hours. It rose sharply and remained at a high of 8-24 hours. After 8-12 hours, CRP did not rise slowly. 2, PCT plasma half-life is short, is an important indicator for observation of efficacy observation and prognosis. PCT plasma time is short, half-life 22-29 hours, good stability in vivo and in vitro, not easy to degrade, PCT test is not affected by clinical drugs (except OKT3), and the severity of positively related infection. Therefore, dynamic observation of changes in plasma PCT concentrations can better judge prognosis and efficacy. CRP has a relatively long half-life and a long-term return to normal levels, which is not suitable for observing prognosis and efficacy. 3. The increase in PCT concentration is not affected by the body's immunosuppressive state. When the body is in a serious bacterial infection or sepsis, the concentration of PCT in the plasma can be seen even if the patient is in an immunosuppressed state or has no obvious clinical manifestations. It is significantly elevated and its degree of increase is positively correlated with the severity of the infection. Although CRP is one of the early indicators of a common systemic inflammatory response, the concentration of CRP in plasma does not increase when the body is immunosuppressed. 4. PCT has specific values for identifying systemic and local bacterial infections. PCT is generally significantly increased in the systemic inflammatory response caused by bacterial susceptibility, especially sepsis, Gram-negative bacilli, and the degree of increase is positively correlated with the severity of infection. After surgery, local infections caused by bacterial and viral infections, PCT, CRP, cytokines, etc. can be increased, but when secondary systemic infection occurs, PCT increases significantly, while CRP, cytokines, etc. decrease. Therefore, changes in CRP and cytokine levels are not consistent with the severity of the infection. Therefore, for systemic infections, the PCT is a more specific indicator. More studies have shown that combined with CRP and PCT testing can improve the sensitivity of the diagnosis of infection. 5. PCT is of great value in the diagnosis and identification of secondary infections of benign and malignant tumors. Serum PCT concentrations in most benign and malignant tumor patients are within the normal range or slightly elevated. When concurrent infections, especially systemic infections, PCT is markedly elevated. high. When there is an inflammatory mass, the PCT positive rate is as high as 100%, and the increase is obvious, which is 10 times higher than the normal level. 6. PCT is an important differential indicator of neonatal sepsis and septic shock. The sensitivity, specificity, accuracy, and positive predictive value of PCT for the diagnosis of neonatal sepsis and septic shock were higher than CRP, but the negative predictive value was lower than CRP. According to reports, when PCT <2.0μgpct=>20μg/L, 96 cases died in 24 cases, and the mortality rate was 25%. 7. Determining PCT concentrations can help doctors determine if antibiotics are needed in patients with respiratory infections. Most respiratory infections are caused by viruses rather than bacteria, but the virus can damage the respiratory tract and cause secondary infections. The determination of PCT concentration can help doctors determine whether antibiotics are needed in patients with respiratory infections to reduce the need for clinically unnecessary antibiotics. According to the Mullard report of the Basel Hospital in Lancet (2004 363:9408), when PCT <0.25 μg/L, antibiotics are not advocated or restricted, such as PCT ≥ 0.25 μg / L or ≥ 0.5 μg / L.