Procalcitonin (PCT) is a hormonally inactive precursor of calcitonin that possesses secondary inflammatory, chemokine, anti-inflammatory, and protective properties. Procalcitonin production during infection and sepsis is independent of calcitonin levels and is closely associated with the release of endotoxins and inflammatory mediators during bacterial infection. Procalcitonin has become the most useful biomarker in the management of infection and sepsis in much of the world.
Production and release of PCT
Procalcitonin is the propeptide of calcitonin, consisting of 116 amino acids. Normally, procalcitonin is encoded by the CALC-1 gene, located on the short arm of chromosome 11 in thyroid C cells. It is cleaved from preprocalcitonin by endopeptidases in the endoplasmic reticulum. Procalcitonin (PCT) is then further broken down into N-PCT, C-terminal calcitonin, and active calcitonin. Under normal physiological conditions, PCT is not typically secreted into the blood, with blood levels below 0.1 ng/ml. However, when bacteria invade the body, blood levels of PCT can rise significantly.
(Data source: Paudel R, et al. Int J Med Sci. 2020)
PCT detection method:
PCT testing is of great significance in the diagnosis, treatment, and prognosis of bacterial infections. By closely monitoring PCT levels, physicians can accurately identify the type and severity of infection. This information enables them to personalize antibiotic therapy based on each patient's specific needs, minimize antibiotic abuse, and develop targeted treatment plans. PCT testing can be performed using a variety of methods, such as immunofluorescence (IF), enzyme-linked immunosorbent assay (ELISA), latex-enhanced turbidimetry (LTA), colloidal gold immunochromatography, and radioimmunoassay (RIA).
(Data source: Huang J, et al. Research. 2024)
(Data source Huang J, et al. Research. 2024)
The clinical value of PCT:
Differentiation of bacterial infection: In clinical practice, evaluating serum PCT concentrations helps identify bacterial infections. A substantial increase in serum PCT indicates a systemic reaction caused by bacterial infection, distinguishing it from other causes such as autoimmune diseases, inflammation, and viral infections, in which PCT levels usually remain at low levels. PCT increases rapidly within hours of severe bacterial infection and has advantages in early diagnosis compared to other inflammatory factors. After surgery, local infections caused by bacteria and viruses may increase PCT, CRP, cytokines, etc. However, when systemic infection occurs secondary to the onset of the infection, PCT increases significantly, while CRP, cytokines, etc. decrease. For systemic infections, PCT is a more specific indicator. More studies have shown that combining CRP and PCT determinations can improve the sensitivity of diagnosing infection.
PCT guides antibiotic treatment: PCT is a classic diagnostic indicator for sepsis. Clinical analysis shows that a blood PCT concentration >2ng/ml can diagnose sepsis caused by bacterial infection. In addition, PCT monitoring can distinguish the infectious course of sepsis. PCT plays a vital role in guiding the rational use of antibiotics, aiming to reduce the abuse of antibiotics. Clinically, when serum PCT < 0.25ng/ml, it is recommended to discontinue antibiotics. If the PCT content drops by more than 80% from the maximum value or drops to the range of 0.25 to 0.5ng/ml, it is also recommended to discontinue antibiotics. On the contrary, when the PCT level exceeds 0.5ng/ml and continues to rise, it indicates that the bacteria may be resistant, and it is strongly recommended to change the type of antibiotic.
(Data source: Vijayan AL, et al. J Intensive Care, 2017)
