Figure 1: Immature Calcitonin | |
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Procalcitonin (PCT) is a peptide precursor of the hormone calcitonin, the latter being involved with calcium homeostasis. It arises once preprocalcitonin is cleaved by endopeptidase. [1] It was first identified by Leonard J. Deftos and Bernard A. Roos in the 1970s. [2] It is composed of 116 amino acids and is produced by parafollicular cells (C cells) of the thyroid and by the neuroendocrine cells of the lung and the intestine.
The level of procalcitonin in the blood stream of healthy individuals is below the limit of detection (0.01 μg/L) of clinical assays. [3] The level of procalcitonin rises in a response to a pro-inflammatory stimulus, especially of bacterial origin. It is therefore often classed as an acute phase reactant. [4] The induction period for procalcitonin ranges from 4–12 hours with a half-life spanning anywhere from 22–35 hours. [5] It does not rise significantly with viral or non-infectious inflammations. In the case of viral infections this is due to the fact that one of the cellular responses to a viral infection is to produce interferon gamma, which also inhibits the initial formation of procalcitonin. [6] With the inflammatory cascade and systemic response that a severe infection brings, the blood levels of procalcitonin may rise multiple orders of magnitude with higher values correlating with more severe disease. [7] However, the high procalcitonin levels produced during infections are not followed by a parallel increase in calcitonin or a decrease in serum calcium levels. [8]
PCT is a member of the calcitonin (CT) superfamily of peptides. It is a peptide of 116 amino acids with an approximate molecular weight of 14.5 kDa, and its structure can be divided into three sections (see Figure 1): [9] amino terminus (represented by the ball and stick model in Figure 1), immature calcitonin (shown in Figure 1 from PDB as the crystal structure of procalcitonin is not yet available), and calcitonin carboxyl-terminus peptide 1. [9] Under normal physiological conditions, active CT is produced and secreted in the C-cells of the thyroid gland after proteolytic cleavage of PCT, meaning, in a healthy individual, that PCT levels in circulation are very low (<.05 ng/mL).[ citation needed ] The pathway for production of PCT under normal and inflammatory conditions are shown in Figure 2. [10] During inflammation, LPS, microbial toxin, and inflammatory mediators, such as IL-6 or TNF-α, induce the CALC-1 gene in adipocytes, but PCT never gets cleaved to produce CT. [10] In a healthy individual, PCT in endocrine cells is produced by CALC-1 by elevated calcium levels, glucocorticoids, CGRP, glucagon, or gastrin, and is cleaved to form CT, which is released to the blood. [10]
PCT is located on the CALC-1 gene on chromosome 11. [9] Bacterial infections induce a universal increase in the CALC-1 gene expression and a release of PCT (>1 μg/mL). [11] Expression of this hormone occurs in a site specific manner. [9] In healthy and non-infected individuals, transcription of PCT only occurs in neuroendocrine tissue, except for the C cells in the thyroid. The formed PCT then undergoes post-translational modifications, resulting in the production small peptides and mature CT by removal of the C-terminal glycine from the immature CT by peptidylglycine α-amidating monooxygenase (PAM). [12] In a microbial infected individual, non-neuroendocrine tissue also secretes PCT by expression of CALC-1. A microbial infection induces a substantial increase in the expression of CALC-1, leading to the production of PCT in all differentiated cell types. [13] The function of PCT synthesized in nonneuroendocrine tissue due to a microbial infection is currently unknown, but, its detection aids in the differentiation of inflammatory processes. [9]
Due to PCT’s variance between microbial infections and healthy individuals, it has become a marker to improve identification of bacterial infection and guide antibiotic therapy. [14] The table below is a summary from Schuetz, Albrich, and Mueller, [14] summarizing the current data of selected, relevant studies investigating PCT in different types of infections.
Legend:
✓ = Moderate evidence in favor of PCT
✓✓ = Good evidence in favor of PCT
✓✓✓ = Strong evidence in favor of PCT
~ = Evidence in favor or against the use of PCT, or still undefined
Infection Type/Setting | Study Design | PCT Cut-Off (ug/L) | PCT Benefit | Conclusion | References |
---|---|---|---|---|---|
Abdominal Infections | observational | 0.25 | ~ | PCT may help exclude ischemia and necrosis in bowel blockage | [15] [16] [17] [18] |
Arthritis | observational | 0.1-0.25 | ✓ | PCT differentiates non-infectious (gout) arthritis from true infection | [19] [20] [21] |
Bacteremic infections | observational | 0.25 | ✓✓ | Low PCT levels help rule out microbial infections | [22] [23] [24] |
Blood stream infection (primary) | observational | 0.1 | ✓✓ | PCT differentiates contamination from true infection | [25] |
Bronchitis | RCT | 0.1-0. 5 | ✓✓✓ | PCT reduces antibiotic exposure without adverse outcomes in the ED | [26] [27] |
COPD exacerbation | RCT | 0.1-0. 5 | ✓✓✓ | PCT reduces antibiotic exposure without adverse outcomes in the ED and hospital | [26] [27] [28] |
Endocarditis | observational | 2.3 | ✓ | PCT is an independent predictor with high diagnostic accuracy for acute endocarditis | [29] [30] |
Meningitis | before-after | 0.5 | ✓ | PCT reduces antibiotic exposure during outbreak of viral meningitis | [31] [32] [33] |
Neutropenia | observational | 0.1-0.5 | ✓ | PCT is helpful at identifying neutropenic patients with systemic bacterial infection | [34] [35] [36] |
Pancreatitis | observational | 0.25-0.5 | ~ | PCT correlates with severity and extent of infected pancreatitis | [37] [38] |
Pneumonia | RCT | 0.1-0. 5; 80-90% ↓ | ✓✓✓ | PCT reduces antibiotic without adverse outcomes exposure in the hospital | [26] [27] [39] [40] [41] [42] |
Postoperative fever | observational | 0.1-0.5 | ✓ | PCT differentiates non-infectious fever from post-operative infections | [43] |
Postoperative infections | RCT | 0.5-1.0; 75-85% ↓ | ✓✓ | PCT reduces antibiotic exposure without adverse outcomes in the surgical ICU | [44] [45] |
Severe sepsis/Shock | RCT | 0.25-0.5; 80-90% ↓ | ✓✓✓ | PCT reduces antibiotic exposure without adverse outcomes in the ICU | [46] [47] |
Upper respiratory tract infections | RCT | 0.1-0.25 | ✓✓ | PCT reduces antibiotic exposure without adverse outcomes in primary care | [48] |
Urinary tract infections | observational | 0.25 | ✓ | PCT correlates with severity of urinary tract infections | [23] [49] |
Ventilator-associated pneumonia | RCT | 0.1-0.25 | ✓✓ | PCT reduces antibiotic exposure without adverse outcomes | [47] [50] |
Measurement of procalcitonin can be used as a marker of severe sepsis caused by bacteria and generally grades well with the degree of sepsis, [51] although levels of procalcitonin in the blood are very low. PCT has the greatest sensitivity (90%) and specificity (91%) for differentiating patients with systemic inflammatory response syndrome (SIRS) from those with sepsis, when compared with IL-2, IL-6, IL-8, CRP and TNF-alpha. [52] Evidence is emerging that procalcitonin levels can reduce unnecessary antibiotic prescribing to people with lower respiratory tract infections. [53] Currently, procalcitonin assays are widely used in the clinical environment. [54]
A meta-analysis reported a sensitivity of 76% and specificity of 70% for bacteremia. [55]
A 2018 systematic review comparing PCT and C-reactive protein (CRP) found PCT to have a sensitivity of 80% and a specificity of 77% in identifying septic patients. In the study, PCT outperformed CRP in diagnostic accuracy of predicting sepsis. [56]
In a 2018 meta-analysis of randomized trials of over 4400 ICU patients with sepsis, researchers concluded that PCT led therapy resulted in lower mortality and lower antibiotic administration. [57]
Immune responses to both organ rejection and severe bacterial infection can lead to similar symptoms such as swelling and fever that can make initial diagnosis difficult. To differentiate between acute rejection of an organ transplant and bacterial infections, plasma procalcitonin levels have been proposed as a potential diagnostic tool. [58] Typically the levels of procalcitonin in the blood remain below 0.5 ng/mL in cases of acute organ rejection, which has been stated previously to be well below the 1 μg/mL typically seen in bacterial infection. [6]
Given procalcitonin is a blood marker for bacterial infections, evidence shows that it is a useful tool in guiding the initiation and duration of antibiotics in patients with bacterial pneumonia and other acute respiratory infections. [59] The use of procalcitonin guided antibiotic therapy leads to lower mortality, less antibiotic usage, decreased side effects due to antibiotics and promotes good antibiotic stewardship. [59] The value in these protocols are evident since a high PCT level correlates with increased mortality in critically ill pneumonia patients especially those with a low CURB-65 pneumonia risk factor score. [60]
In adults with acute respiratory infections, a 2017 systematic review found that PCT-guided therapy reduced mortality, reduced antibiotic use (2.4 fewer days of antibiotics) and led to decreased adverse drug effects across a variety of clinical settings (ED, ICU, primary care clinic). [59]
Procalcitonin-guided treatment limits antibiotic exposure with no increased mortality in patients with acute exacerbation of chronic obstructive pulmonary disease. [61]
Using procalcitonin to guide protocol in acute asthma exacerbation led to reduction in prescriptions of antibiotics in primary care clinics, emergency departments and during hospital admission. This was apparent without an increase in ventilator days or risk of intubation. Be that acute asthma exacerbation is one condition that leads to overuse of antibiotics worldwide, researchers concluded that PCT could help curb over-prescribing. [62]
PCT serves a marker to help differentiate acute respiratory illness such as infection from an acute cardiovascular concern. It also has value as a prognostic lab value in patients with atherosclerosis or coronary heart disease as its levels correlate with the severity of the illness. [63]
The European Society of Cardiology recently released a PCT-guided algorithm for administering antibiotics in patients with dyspnea and suspected acute heart failure. The guidelines use a cut off point of .2 ng/mL and above as the point at which to give antibiotics. [64] This coincides with a 2017 review of literature which concluded that PCT can help reduce antibiotic overuse in patients presenting with acute heart failure. [65] In regards to mortality, a meta analysis of over 5000 patients with heart failure concluded that elevated PCT was reliable in predicting short term mortality. [66]
Blood procalcitonin levels can help confirm bacterial meningitis and. if negative, can effectively rule out bacterial meningitis. This was shown in a review of over 2000 patients in which PCT had a sensitivity of 86% and a specificity of 80% for cerebrospinal fluid PCT. Blood PCT measurements proved superior to cerebrospinal fluid PCT with a sensitivity of 95% and a specificity of 97% as a marker for bacterial meningitis. [67]
In acute meningitis, serum PCT is useful as a biomarker for sepsis. It can also be of use in determining viral meningitis versus bacterial meningitis. These findings are the result of a 2018 literature review. [68] This followed a 2015 meta analysis that showed that PCT had a sensitivity of 90% and a specificity of 98% in judging viral versus bacterial meningitis. PCT also outperformed other biomarkers such as C-reactive protein. [69]
Evidence shows that an elevated PCT above .5 ng/mL could help diagnose infectious complications of inflammatory bowel disease such as abdominal abscesses, bacterial enterocolitis etc. PCT can be effective in early recognition of infections in IBD patients and decisions on whether to prescribe antibiotics. [70]
Patients with chronic kidney disease and end-stage renal disease are at higher risk for infections, and procalcitonin has been studied in these populations, who often have higher levels. Procalcitonin can be dialyzed, and so levels are dependent upon when patients receive hemodialysis. While there is no formally accepted cutoff value for patients undergoing HD, using a value of greater or equal to 0.5 ng/mL yielded a sensitivity of 97-98% and a specificity of 70-96%. [71]
PCT, possibly together with CRP, is used to corroborate the MELD score. [72] [73]
PCT at a cutoff value of .5 ng/mL was effective at ruling in septic arthritis in an analysis of over 8000 patients across 10 prospective studies. PCT had a sensitivity of 54% and specificity of 95%. The study also concluded that PCT outperforms C-reactive protein in differentiating septic arthritis from non-septic arthritis. [74]
A 2016 literature review showed that PCT has good value in diagnosing infections in oncologic patients. Moreso, it is especially effective in diagnosing major life threatening episodes in cancer patient such as bacteremia and sepsis. [75] Procalcitonin is reliable to monitor recurrence of medullary thyroid carcinoma. In detecting cancer recurrence, PCT had a sensitivity and specificity of 96% and 96% respectively. [76]
In a meta analysis of 17 studies, PCT had a sensitivity of 85% and a specificity of 54% in diagnosing sepsis in neonates and children. The PCT cut off used was between 2-2.5 ng/mL. [77]
In children presenting with fever without an apparent source, a PCT level of .5 ng/mL had a sensitivity of 82% and specificity of 86%. At a 5 ng/mL value, the sensitivity and specificity were 61% and 94%. PCT can help the clinical decision making while identifying invasive bacterial infection in children with unexplained fever. [78]
PCT levels correlate with the degree of illness in pediatric patients with sepsis or urinary tract infections making it effective as a prognostic lab value in these patients. [79]
Procalcitonin guided cessation of antibiotic use reduces duration of antibiotic exposure and lowers mortality in critically ill patients in the Intensive Care Unit. [80]
In adult emergency department patients with respiratory tract illnesses, PCT-guided treatment groups had reduced antibiotic use. [81] PCT references ranges are also used to determine the likelihood a patient has systemic infection (sepsis), thereby reducing incidence of unnecessary antibiotic use in cases where sepsis is unlikely. [82]
Although some literature differs in antibiotic cessation requirements the general consensus is stopping antibiotics when procalcitonin levels fall 80% below peak or below 0.5 μg/L at day five or later during antibiotic therapy. [83]
Excessive overdose on amphetamine or its analogs can induce systemic inflammation; in a case report of amphetamine overdose, without bacterial infection, significant elevations in procalcitonin were observed. [84]
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity of the condition is variable.
Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs.
Bloodstream infections (BSIs) are infections of blood caused by blood-borne pathogens. The detection of microbes in the blood is always abnormal. A bloodstream infection is different from sepsis, which is characterized by severe inflammatory or immune responses of the host organism to pathogens.
Septic shock is a potentially fatal medical condition that occurs when sepsis, which is organ injury or damage in response to infection, leads to dangerously low blood pressure and abnormalities in cellular metabolism. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) defines septic shock as a subset of sepsis in which particularly profound circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than with sepsis alone. Patients with septic shock can be clinically identified by requiring a vasopressor to maintain a mean arterial pressure of 65 mm Hg or greater and having serum lactate level greater than 2 mmol/L (>18 mg/dL) in the absence of hypovolemia. This combination is associated with hospital mortality rates greater than 40%.
Bronchiolitis is inflammation of the small airways in the lungs. Acute bronchiolitis is due to a viral infection usually affecting children younger than two years of age. Symptoms may include fever, cough, runny nose, wheezing, and breathing problems. More severe cases may be associated with nasal flaring, grunting, or the skin between the ribs pulling in with breathing. If the child has not been able to feed properly, signs of dehydration may be present.
Lower respiratory tract infection (LRTI) is a term often used as a synonym for pneumonia but can also be applied to other types of infection including lung abscess and acute bronchitis. Symptoms include shortness of breath, weakness, fever, coughing and fatigue. A routine chest X-ray is not always necessary for people who have symptoms of a lower respiratory tract infection.
Acute pancreatitis (AP) is a sudden inflammation of the pancreas. Causes, in order of frequency, include: a gallstone impacted in the common bile duct beyond the point where the pancreatic duct joins it; heavy alcohol use; systemic disease; trauma; and, in children, mumps. Acute pancreatitis may be a single event; it may be recurrent; or it may progress to chronic pancreatitis and/or pancreatic failure.
Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system, and joints of humans. It causes the infection of the host cell by sticking to the host cell using trimeric autotransporter adhesins.
Carbapenems are a class of very effective antibiotic agents most commonly used for treatment of severe bacterial infections. This class of antibiotics is usually reserved for known or suspected multidrug-resistant (MDR) bacterial infections. Similar to penicillins and cephalosporins, carbapenems are members of the beta-lactam antibiotics drug class, which kill bacteria by binding to penicillin-binding proteins, thus inhibiting bacterial cell wall synthesis. However, these agents individually exhibit a broader spectrum of activity compared to most cephalosporins and penicillins. Furthermore, carbapenems are typically unaffected by emerging antibiotic resistance, even to other beta-lactams.
Norfloxacin, sold under the brand name Noroxin among others, is an antibiotic that belongs to the class of fluoroquinolone antibiotics. It is used to treat urinary tract infections, gynecological infections, inflammation of the prostate gland, gonorrhea and bladder infection. Eye drops were approved for use in children older than one year of age.
Ventilator-associated pneumonia (VAP) is a type of lung infection that occurs in people who are on mechanical ventilation breathing machines in hospitals. As such, VAP typically affects critically ill persons that are in an intensive care unit (ICU) and have been on a mechanical ventilator for at least 48 hours. VAP is a major source of increased illness and death. Persons with VAP have increased lengths of ICU hospitalization and have up to a 20–30% death rate. The diagnosis of VAP varies among hospitals and providers but usually requires a new infiltrate on chest x-ray plus two or more other factors. These factors include temperatures of >38 °C or <36 °C, a white blood cell count of >12 × 109/ml, purulent secretions from the airways in the lung, and/or reduction in gas exchange.
Respiratory tract infections (RTIs) are infectious diseases involving the lower or upper respiratory tract. An infection of this type usually is further classified as an upper respiratory tract infection or a lower respiratory tract infection. Lower respiratory infections, such as pneumonia, tend to be far more severe than upper respiratory infections, such as the common cold.
Meningococcal disease describes infections caused by the bacterium Neisseria meningitidis. It has a high mortality rate if untreated but is vaccine-preventable. While best known as a cause of meningitis, it can also result in sepsis, which is an even more damaging and dangerous condition. Meningitis and meningococcemia are major causes of illness, death, and disability in both developed and under-developed countries.
Eosinopenia is a condition where the number of eosinophils, a type of white blood cell, in circulating blood is lower than normal. Eosinophils are a type of granulocyte and consequently from the same cellular lineage as neutrophils, basophils, and mast cells. Along with the other granulocytes, eosinophils are part of the innate immune system and contribute to the defense of the body from pathogens. The most widely understood function of eosinophils is in association with allergy and parasitic disease processes, though their functions in other pathologies are the subject of ongoing research. The opposite phenomenon, in which the number of eosinophils present in the blood is higher than normal, is known as eosinophilia.
Pneumococcal infection is an infection caused by the bacterium Streptococcus pneumoniae.
Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, intense headache, vomiting and neck stiffness and occasionally photophobia.
Neonatal sepsis is a type of neonatal infection and specifically refers to the presence in a newborn baby of a bacterial blood stream infection (BSI) in the setting of fever. Older textbooks may refer to neonatal sepsis as "sepsis neonatorum". Criteria with regards to hemodynamic compromise or respiratory failure are not useful clinically because these symptoms often do not arise in neonates until death is imminent and unpreventable. Neonatal sepsis is divided into two categories: early-onset sepsis (EOS) and late-onset sepsis (LOS). EOS refers to sepsis presenting in the first 7 days of life, with LOS referring to presentation of sepsis after 7 days. Neonatal sepsis is the single most common cause of neonatal death in hospital as well as community in developing country.
Neonatal infections are infections of the neonate (newborn) acquired during prenatal development or within the first four weeks of life. Neonatal infections may be contracted by mother to child transmission, in the birth canal during childbirth, or after birth. Neonatal infections may present soon after delivery, or take several weeks to show symptoms. Some neonatal infections such as HIV, hepatitis B, and malaria do not become apparent until much later. Signs and symptoms of infection may include respiratory distress, temperature instability, irritability, poor feeding, failure to thrive, persistent crying and skin rashes.
Enitan Carrol is a British physician and Professor of Clinical Infection, Microbiology and Immunology. Carrol studies the mechanisms that underpin bacterial infection. In 2020 she was featured in Nicola Rollock's exhibition Phenomenal Women: Portraits of UK Black Female Professors.
Presepsin is a 13-kDa-cleavage product of CD14 receptor.
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