Calcitoninogen (PCT) assay and clinical significance I. Overview PCT is a non-hormonally active precalcitonin peptide, consisting of 116 amino acids and a glycoprotein with a molecular weight of 13 KD. PCT has a half-life of 25-30 hours and is very stable in vitro. Plasma PCT levels in healthy individuals are extremely low. PCT selectively responds to systemic bacterial, fungal, and parasitic infections, but not to sterile inflammation and viral infections or only mildly. Many scholars have found that PCT levels are abnormally increased in systemic bacterial, fungal and parasitic infections, and the degree of increase correlates with the severity and prognosis of the infection, which is of high clinical value in the differential diagnosis, prognosis and efficacy observation of systemic bacterial infections and sepsis. The increase in PCT concentration signifies an ongoing inflammatory response, the use of adequate antibiotics, treatment with inflammatory foci removal, etc. A decrease in PCT values proves that the treatment plan is correct and the prognosis is good, and conversely changes the treatment plan. PCT provides help and support for the differential diagnosis of all inflammatory diseases of unknown etiology, such as bacterial versus toxigenic acute adult respiratory distress syndrome (ARDS); biliary versus toxigenic pancreatitis; bacterial versus viral meningitis; microbially induced fever versus non-bacterial fever, especially the diagnosis of fever-until- investigation (FOU), viral infection or auto The differentiation of acute bacterial infections in immune dysregulated versus immunosuppressed conditions, the differentiation of the etiology of fever, such as in tumor patients induced by tumor lysates or chemotherapy versus bacterial, fungal or other infectious etiologies, the early diagnosis of systemic bacterial infections in neonates and infants versus acute fever due to sepsis; postoperative routine, including postoperative infection warning and medication monitoring, postoperative resection of infected foci (e.g., peritonitis, soft tissue Postoperative routine, including postoperative infection warning and medication monitoring, postoperative treatment guidance after resection of infected foci (e.g., peritonitis, soft tissue infections), monitoring of peritonitis, anastomotic leaks, and disease processes without typical abdominal symptoms; post-transplant monitoring, pre-transplant exclusion of acute bacterial or other infections, identification of acute organ rejection, acute viral, bacterial and fungal infections; monitoring of patients in the ICU for long periods of time and patients on long-term mechanical ventilation, monitoring of disease processes and guidance of treatment; monitoring of high-risk patients, early access to information about complications and internal environmental decline. Many clinical studies have demonstrated the high value of PCT in different medical fields for diagnosis and guiding treatment, providing additional information in differential diagnosis and control of infections and severe inflammation compared to the currently applied diagnostic indicators. As clinical practicability studies continue to progress and clinical data accumulate, PCT will become consensus as a routine indicator for the auxiliary and differential diagnosis of systemic bacterial infections and sepsis, and will be widely used. The molecular biology of PCT is derived from a single copy gene (the same gene as calcitonin gene-related peptide) located on chromosome 11 (11P15,4). The gene consists of 2800 base pairs, with 6 exons and 5 introns, and is approximately 7.6 Kb in length. mRNA for PCT is produced by specific editing after transcription, and then translated into calcitonin precursor (Pre-PCT), which is formed in the Golgi complex and secretory vesicle by a series of hydrolytic enzymes to form PCT amino acid polypeptide (aminoPCT), calcitonin (CT) and The 21 amino polypeptides at the carboxyl terminus (CT: CCP-1) are formed. Serum PCT and its components are increased in patients with medullary thyroid tumors or other neuroendocrine tumors, and the relative content of the components is also changed. In some patients with non-thyroidal injuries such as chronic renal failure, inhalation burns, acute bacterial infections, stroke, sepsis, etc., serum PCT and its components are also increased, some even exponentially, while CT is slightly elevated, indicating that in addition to the secretion and storage of PCT by medullary thyroid cells, there are still other cells with these functions. Possible biological mechanisms of elevated serum PCT: The target cells (PBMCs, etc.) secrete PCT in response to various sepsis-related factors in LPS, and this emergency secretion exceeds the post-transcriptional process of cells (from Pro-CT to aminoPCT, CT, CT:CCP-1) or the post-conversion process lacks the necessary hydrolytic enzymes, resulting in the experimentally observed PCT The level of CT is unchanged or slightly increased. Fourth, the detection methods and normal reference value range at present, in addition to time-consuming and not easy to automate the gel chromatography and high performance liquid chromatography analysis, detection of PCT more specific and sensitive analytical methods are: double antibody sandwich immunochemical luminescence (double antibody sandwich method) and radioimmunoassay (RIA). The double antibody sandwich method uses dual monoclonal antibodies, one as a capture antibody directly binding to amino acid residues 96-106 of PCT, i.e. immature CT: CCP-1 part, and the other as a tracer antibody directly binding to amino acid residues 70-76 of PCT, i.e. immature CT molecules, with synthetic PCT as the standard. The method is relatively specific and non-cross-reactive, with a minimum detection of 10pg?ml-1l and a linear range of 10-60pg?ml-1 for the standard curve. intra- and inter-batch coefficients of variation are 7G and 8G, respectively. commercial reagents are available for this method, which requires less time and is easily automated, but the method cannot detect PCT in normal human serum. the RIA uses a polyclonal antibody specific for synthetic aminoPCT RIB7 acts directly on the aminoPCT portion of PCT, so RIA can detect both free PCT and bound PCT, as well as calcitonin gene-related precursor (Pro-CGRP), with a plausible sensitivity of 4 pg?ml-1. The linear range is 10-77 pg?ml-1, and the bound free ratio of 50G The linear range is 10-77 pg?ml-1 and the binding free ratio of 50G is 140 pg?ml-1. This method can detect normal human serum PCT, so it is more sensitive than the double antibody sandwich method, another advantage is that RIA shows a positive correlation with the duration of the patient’s disease (r=0.47,p=0.071). the disadvantage of RIA is the longer time required. V. Application of PCT assay in different clinical departments 1. Hematology-Oncology Severe infection is a fatal complication in patients with immunosuppression and neutropenia due to chemotherapy or bone marrow transplantation, and there are multiple causes of fever during chemotherapy. Fever is usually a symptom of a bacterial, viral or fungal infection, but sometimes it is a reaction to the drugs used during treatment. Fever due to tumor cell lysis is more common, and the source of fever remains unknown in most cases. PCT helps to make a definitive diagnosis of systemic infections caused by bacteria and fungi. Even in chemotherapy patients, PCT can make a reliable detection and assessment for the presence of septic infection. Patients with neutropenia often lack specific symptoms of inflammation. PCT in immunosuppressed and neutropenic patients shows similar results to those observed in patients without immunosuppression. Its diagnostic value has been significantly better than that of CRP and cytokines. Elevated PCT concentrations have a high diagnostic yield for bacterial systemic infections. If septic shock occurs after allografting, extremely elevated plasma PCT concentrations indicate a poor prognosis. 2. Anesthesiology Postoperative septic infection and multiorgan failure remain the most common cause of death in intensive care units today. Plasma PCT concentrations are usually within the normal range for minor and major surgery, such as major abdominal or thoracic surgery, and are often elevated within 1-2 days postoperatively, usually 0.5-2.0 ng?ml, occasionally exceeding 5 ng?ml, a condition that often decreases to normal levels within a few days with a 24-hour half-life rate. Thus high or persistent high levels of PCT due to infection after surgery can be easily identified. In 12-24 hours after compound trauma, PCT is moderately elevated up to 2.0 ng?ml, and in severe lung or chest trauma, PCT can reach 5 ng?ml, which generally decreases to normal range with a half-life rate if there is no infection complication. 3. Internal medicine Internal medicine intensive care The problems in medical care often revolve around the diagnosis of infection and the differential diagnosis of whether it is related to infection. The validity of the evaluation of the severity of inflammation and its treatment outcome is a necessary prerequisite for an effective treatment plan. PCT selectively responds to systemic bacterial infections, similar bacterial infections and protozoal infections, while it does not respond or responds only mildly to sterile inflammatory and viral infections. Therefore, PCT can be easily applied in the differential diagnosis of common diseases and syndromes in internal medicine, such as: differential diagnosis of infectious and non-infectious etiology of respiratory distress in adults; differential diagnosis of infected necrosis and aseptic necrosis in pancreatitis; identification of fever in infections, such as in patients with oncological and hematological diseases receiving chemotherapy; differential diagnosis of chronic autoimmune diseases in patients receiving immunosuppressive acute deterioration versus rheumatic disease with systemic bacterial infection; differential diagnosis of bacterial meningitis versus viral meningitis; clarify the presence of life-threatening bacterial and fungal infections in patients with neutropenia receiving chemotherapy; clarify the presence of severe bacterial and fungal infections in organ transplant patients receiving immunosuppressive therapy, and for differential diagnosis of infection and transplant rejection. 4. transplantation surgery Successful transplantation is often challenged by complications such as severe infections.31G patients develop infections within the first year after transplantation, and symptoms of infection can be masked by acute or chronic rejection, so that early and reliable diagnosis of infections that occur during the rejection period cannot be made. The use of PCT testing in organ transplant patients allows for early introduction of treatment thereby improving survival rates as well as shortening the length of hospital stay. PCT is used to diagnose infections in transplant patients, where immunosuppressive therapy severely compromises the ability to fight infection. PCT >0.1 ng?ml in the early stages of infection has a sensitivity of 77 G and a specificity of 100 G. Monthly monitoring of PCT concentrations provides a reliable evaluation of the efficacy of antimicrobial therapy. PCT is used in organ rejection, and one of the main tasks of post-transplant monitoring is to be able to clearly distinguish between infection and organ rejection. Since PCT release is not caused by acute or chronic organ rejection stimuli, a high PCT concentration can be considered as the presence of infection. If the PCT concentration exceeds 10 ng?ml, 98G is likely to be an infection rather than organ rejection. 5. Neonatology Many diseases have no specific manifestation in preterm and neonatal infants. Neonatal sepsis cannot be reliably diagnosed by hematological tests and traditional laboratory indicators and acute phase proteins. The results of microbiological tests take several days and negative results do not exclude the presence of clinical infection and the high mortality associated with it. PCT is an improved laboratory indicator with high sensitivity and specificity for the diagnosis of postnatal sepsis in newborns compared to other diagnostic indicators of inflammation. PCT can also be used for the evaluation of the outcome of treatment. Age-dependent normal values of PCT in preterm and neonatal infants: PCT reaches its physiological peak of 21 ng?ml at 24-30 hours after birth, but the mean value is only 2 ng?ml,. From the third day after birth, the normal reference value of PCT is the same as in adults. PCT is a highly specific indicator of neonatal sepsis: in preterm infants and neonatal sepsis infections, PCT can make an earlier and more specific diagnosis than traditional methods, and its sensitivity and specificity for neonatal diagnosis can reach 100G. 6. Pediatrics Pediatric hyperthermia is often difficult to distinguish between different sources of infection by clinical means, and this problem can particularly affect the accurate diagnosis of patients given immunosuppressive therapy for hematologic and oncologic diseases. This problem particularly affects the accurate diagnosis of patients given immunosuppressive therapy for hematologic and neoplastic diseases. Moreover, many diseases are associated with secondary immunopathological changes, such as rheumatic fever, making it difficult to distinguish them from primary bacterial infections in children. PCT has a high sensitivity and specificity for the differential diagnosis of bacterial and viral infections. Since there are essential differences in the treatment of bacterial and viral infections, PCT can provide valuable information for the treatment of patients with non-specific symptoms of infection. Detection of proteins and cells in the cerebrospinal fluid is not helpful in identifying pediatric bacterial meningitis from viral meningitis, and there is significant crossover between many of the tests with specificity. High PCT concentrations are only seen in bacterial meningitis; whereas in viral meningitis PCT remains within the normal range (no PCT is detected in the cerebrospinal fluid). Daily monitoring of PCT concentrations by time allows for reliable evaluation of treatment outcomes. 7. Surgery Sepsis infection and multi-organ failure are fatal postoperative complications for which there is still no cure, despite the great progress of modern medicine. Early and accurate postoperative diagnosis of septic infections not caused by pre-existing disease or surgical trauma itself is the key to successful treatment. PCT concentrations are not affected by pre-existing diseases such as cancer, allergic reactions or autoimmune diseases, and PCT is significantly better than other inflammatory factors such as CRP and cytokines, making it an objective and easily detectable indicator with unique diagnostic advantages over even more invasive, risky and costly diagnostic methods such as fine needle aspiration pathology. Application of postoperative PCT: PCT is closely related to the development and course of serious bacterial and septic infections and can accurately reflect whether the source of infection causing the lesion (e.g., peritonitis) has been eradicated. Daily monitoring of PCT concentrations provides a reliable evaluation of the outcome of treatment. PCT can be used for monitoring of surgical trauma or compound trauma. PCT is used in patients undergoing cardiac surgery, which uses a heart-lung machine, even if the patient has diseases such as leukocytosis, neutrophilia, eosinophilia or inadequate elevation of CRP, PCT concentrations are usually not elevated or are only slightly elevated, so PCT is well suited for the detection of sepsis. VI. Prospects With the continuous in-depth clinical and laboratory research and the accumulation of a large amount of clinical data, PCT will become a consensus as a routine laboratory indicator for the auxiliary and differential diagnosis of systemic bacterial infection and sepsis and will be promoted. In addition, the exact source and pathophysiological role of PCT in systemic bacterial infections and sepsis are still waiting for our further in-depth study. VII. REFERENCES 1. Karzai W, Oberhoffer M, Meier-hellmann A, et al. Procalcitonin -A new indicater of the systemic response to severe infections. Infection, 1997, 25:329 2. Gebdrek D, Assicot M, Raymond S, et al. Procalcitonin as a marker for early diagnosis of neonatal infection. J Pediatr, 1996, 128: 570 3. Oberhoffer M, Stonans I, Russwurm S, et al. Procalcitonin expression in Human PeriPheral blood mononuclear cells and its mudalution by lipopolysaccharides and sepsis related cytokines in vitro. J Lab Clin Med, 1999, 134:49 4. Michael Meisner. Procalcitonin-A new marker of severe infection and sepsis. Thleme, 2000, 179 5. Hergert M, Kestln HG, Scherkus, et al. Procalcitonin in patients with the ACCP/SCCM consensus definitions than other specific markers of the inflammatory polytrauma. Clin Lab 1998, 44:659 6. Mersner M, Tschaikowsky K, Palmaers T, et al. PCT and CRP : Comparison of plasma concentrations at different SOFA-scores during the course of sepsis and MODS. Shock (Abstract) 1997, 8:47?