What is procalcitonin (PCT)?

Updated: Jul 30, 2019
  • Author: Jiun-Lih Jerry Lin, MBBS, MS(Orth); Chief Editor: Eric B Staros, MD  more...
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Procalcitonin (PCT) is a biomarker that exhibits greater specificity than other proinflammatory markers (eg, cytokines) in identifying sepsis and can be used in the diagnosis of bacterial infections.

Procalcitonin is also produced by the neuroendocrine cells of the lung and intestine and is released as an acute-phase reactant in response to inflammatory stimuli, especially those of bacterial origin. This raised procalcitonin level during inflammation is associated with bacterial endotoxin and inflammatory cytokines. [1, 2] Increased levels of serum procalcitonin in response to viral infections and noninfectious inflammatory stimuli such as autoimmune disease and chronic inflammatory processes are much less pronounced, rarely exceeding 0.5 ng/mL. [5, 6] Procalcitonin released as an acute-phase reactant does not result in increased serum calcitonin levels.

The physiologic importance and regulation of procalcitonin production is not well understood. Several hypotheses suggest that procalcitonin may be involved in metabolism of calcium, cytokine network, and modulation of nitric oxide (NO) synthesis, as well as pain-relieving effects. [7] No enzymes in the plasma break down procalcitonin. Therefore, if procalcitonin enters the circulation, it remains unchanged, with a half-life of around 30 hours, with no evidence that serum procalcitonin binds to cellular receptors of calcitonin or any specific procalcitonin receptors. [7]

Studies have shown that, in patients with sepsis, higher procalcitonin levels are associated with a greater risk of progression to severe sepsis and septic shock, worsening the survival prognosis. Local bacterial infections and abscesses do not significantly raise procalcitonin levels. [6, 8, 9] Procalcitonin levels fall with successful treatment of severe bacterial infection and severe noninfectious inflammatory stimuli. Persistent or recurrent procalcitonin elevation in the latter setting should prompt suspicion of secondary infection.

A study by Bassetti et al indicated that procalcitonin can aid in early demonstration of the etiology of bacterial infection, finding that it has moderate value in detecting Gram-negative bacteremia, particularly that resulting from Enterobacteriaceae, within 24 hours of infection. The investigators reported that procalcitonin levels were higher in patients infected with Gram-negative bacteria (26.1 ng/mL) than in those with with Gram-positive or fungal infection (6.9 and 3.3 ng/mL, respectively). Mean C-reactive protein values, however, showed no such differences in value. [10]

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