Procalcitonin (procalcitonin) is a glycoprotein composed of 116 amino acids with a molecular weight of about 12.7kD. It is a propeptide of calcitonin with no hormone activity. PCT is expressed by neuroendocrine cells (including C cells of thyroid, lung and pancreas tissues) and decomposed into (immature) calcitonin, carboxyl-terminal peptide and amino-terminal peptide.
1. Biological characteristics of PCT Stable: PCT is very stable in serum/whole blood/plasma. When placed at room temperature for 24 hours, PCT plasma concentration only decreases by 12%. Placed at 4 degrees Celsius for 24 hours, only reduced by 6% Fast: It can be measured 3 hours after the infection starts and reaches the peak value after 6-13 hours. High peak value: the peak value can reach up to 1000ng/mL; and the half-life is close to 24 hours. Normal conditions and infections: The concentration in the blood of healthy people is very low, <0.05ng/mL; during bacterial infection, PCT can be generated and released into the blood circulation, and the concentration increases rapidly. Note: Viral infection and non-specific inflammation will not cause an increase in PCT levels, but bacterial infection, severe shock and multiple organ failure syndrome can cause a significant increase in PCT levels, and the extent of the increase is related to the severity of the disease and the patient. prognosis is closely related.
2. PCT physiological functions The main biological effects of PCT: 1. The role of secondary inflammatory factors; 2. The role of chemokines; 3. Anti-inflammatory and protective effects. PCT is an immune substance. When there is a local infection, PCT regulates the accumulation of monocytes in a short period of time, and is released locally to act as a chemokine, further attracting and activating monocytes to pass through the tissue. The feedback is weakened due to the appearance of PCT. Allowing cells to stay at the site of infection, at which point PCT levels may not increase or may not increase significantly; In conditions such as systemic severe bacterial infection, PCT is in direct contact with activated monocytes, and adipocytes initiate the synthesis of PCT and calcitonin gene-related peptide. On the one hand, in the endothelial smooth muscle cells, PCT inhibition can induce nitric oxide. Activation of synthase (iNOs) can cause NO-regulated vasodilation during inflammation, producing effects at sites far away from inflammation; on the other hand, in smooth muscle cells that have been in contact with pro-inflammatory mediators, PCT stimulates the production of iNOs , produces an effect at the inflammatory site; at this time, the level of PCT increases significantly.
3. Expert consensus on procalcitonin
Bacterial meningitis: Elevated serum levels of PCT differentiate severe bacterial meningitis from viral meningitis ---2004 Practice guidelines for the management of bacterial meningitis Pleural infection in children: PCT identifies whether pleural infection in children is bacterial or viral ---2013 BTS guidelines for the management of pleural infection in children
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