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Procalcitonin (PCT) is a precursor of the hormone calcitonin, which is involved with calcium homeostasis, and is produced by the C-cells of the thyroid gland. It is there that procalcitonin is cleaved into calcitonin, katacalcin and a protein residue. It is not released into the blood stream of healthy individuals.
Procalcitonin is said to distinguish between bacterial and non-bacterial causes of inflammation. A meta-analysis of three studies, dominated by a pediatric study, reported that the sensitivity for differentiating bacterial from viral infections was 92% with specificity of 73%.
With the derangements that a severe infection with an associated systemic response brings, the blood levels of procalcitonin may rise to 100 ng/ml. In blood serum, procalcitonin has a half-life of 25 to 30 hours.
There are two commercial kits for measuring the PCT. The Kryptor assay has a lower limit of detection of 0.06 μg/L while the LUMI kit has a lower limit of detection of 0.3–0.5 μg/L. The Kryptor kit is thought by some to be better and more sensitive than the the LUMI test. However, comparisons of their ability to prognosticate pneumomia as compared to using the c-reactive protein have conflicted with PCT by Kryptor being similar to or better than the c-reactive protein and PCT by LUMI being betterthan the c-reactive protein.
Diagnosis and prognosis of sepsis
Measurement of procalcitonin can be used as a marker of severe sepsis and generally grades well with the degree of sepsis, although levels of procalcitonin in the blood are very low. PCT has the greatest sensitivity (85%) and specificity (91%) for differentiating patients with SIRS from those with sepsis, when compared with IL-2, IL-6, IL-8, CRP and TNF-alpha. However, the test is not routinely used and has yet to gain widespread acceptance.
In a comprehensive meta-analysis in 2007 the diagnostic accuracy of procalcitonin as a marker to differentiate sepsis from other non-infectious causes of systemic inflammatory responses was estimated including 18 studies (14 phase 2 and 4 phase 3 studies).  In this review the overall diagnostic performance of procalcitonin was low. The authors concluded that procalcitonin cannot reliably differentiate sepsis from other non-infectious causes of systemic inflammatory response syndrome in critically ill adult patients and should not be used as often as it is currently done in the critical care setting.
Diagnosis of bacteremia
Prognosis of respiratory tract infection
A randomized controlled trial of patients with respiratory tract infections (more common diagnoses were rhinosinusitis and bronchitis), procalcitonin guided therapy reduces antibiotic use without compromising patient outcome.
Diagnosis of pneumonia
Procalcitonin has been studied for the diagnosis of pneumonia.
Prognosis of pneumonia
A cluster randomized controlled trial found that the procalcitonin level can help guide antibiotic therapy in patients with pneumonia. In this trial, "on the basis of serum procalcitonin concentrations, use of antibiotics was more or less discouraged (<0.1 microg/L or <0.25 microg/L) or encouraged (> or =0.5 microg/L or > or =0.25 microg/L), respectively".. However, a nonrandomized, observational study reported "limited, prognostic value" of the procalcitonin.
- The procalcitonin level may be able to accurately lower the estimated risk among patients thought to be high risk by the clinical prediction rules In this study of 1,651 patients, the area under the receiver operating characteristic curve (AUC) for predicting death was 0.83 for the pneumonia severity index alone and insignificantly rose to 0.85 when combined with the procalcitonin.
- The procalcitonin level may add to the CURB-65. In this study of 1,671 patients, the area under the receiver operating characteristic curve (AUC) for predicting death was 0.79 for the CURB-65 alone and significantly rose to 0.83 when combined with the procalcitonin.
- The procalcitonin level may not add to the CURB-65 and the pneumonia severity index. In this study of 453 patients, the area under the receiver operating characteristic curve (AUC) for predicting death was 0.82 for the CURB-65 alone and insignificantly rose to 0.84 when combined with the procalcitonin. The C-reactive protein may add to the clinical prediction rules.
Trails of guiding antibiotic decisions
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- Bouadma L, Luyt CE, Tubach F, Cracco C, Alvarez A, Schwebel C et al. (2010). "Use of procalcitonin to reduce patients' exposure to antibiotics in intensive care units (PRORATA trial): a multicentre randomised controlled trial.". Lancet. DOI:10.1016/S0140-6736(09)61879-1. PMID 20097417. Research Blogging.
- Schuetz P, Christ-Crain M, Thomann R, Falconnier C, Wolbers M, Widmer I et al. (2009). "Effect of procalcitonin-based guidelines vs standard guidelines on antibiotic use in lower respiratory tract infections: the ProHOSP randomized controlled trial.". JAMA 302 (10): 1059-66. DOI:10.1001/jama.2009.1297. PMID 19738090. Research Blogging.
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- Shehabi Y, Sterba M, Garrett PM, Rachakonda KS, Stephens D, Harrigan P et al. (2014). "Procalcitonin algorithm in critically ill adults with undifferentiated infection or suspected sepsis. A randomized controlled trial.". Am J Respir Crit Care Med 190 (10): 1102-10. DOI:10.1164/rccm.201408-1483OC. PMID 25295709. Research Blogging.
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- Procalcitonin - web site of the manufacturer of the PCT assay.