Not extremely well! Although a recent multicenter prospective study in adult hospitalized patients reported that the median procalcitonin (PCT) concentration was significantly lower for community-acquired pneumonia (CAP) caused by viral compared to bacterial pathogens, normal PCT values at <0.1 ug/ml and <0.25 ug/ml were also found in 12.4% and 23.1% of typical bacterial cases, respectively1.
This means that we could potentially miss about a quarter of CAP cases due to typical bacterial causes if we use the <0.25 ug/ml threshold (<0.20 is ug/ml has often been used to exclude sepsis2). Based on the results of these and another study3, no threshold for PCT can reliably distinguish bacterial from viral etiologies of CAP.4 Clinical context is essential in interpreting PCT levels!
Can PCT distinguish Legionella from other atypical bacterial causes of CAP (eg, caused by Mycoplasma or Chlamydophila)? The answer is “maybe”! Legionella was associated with higher PCT levels compared to Mycoplasma and Chlamydophila in one study1, but not in another3.
For a related pearl on P4P go to https://pearls4peers.com/2017/07/01/should-i-order-serum-procalcitonin-on-my-patient-with-suspected-infection
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- Self WH, Balk RA, Grijalva CG, et al. Procalcitonin as a marker of etiology in adults hospitalized with community-acquired pneumonia. Clin Infect Dis 2017;65:183-90. https://www.ncbi.nlm.nih.gov/pubmed/28407054
- Meisner M. Update on procalcitonin measurements. Ann Lab Med 2014;34:263-73.
- Krüger S, Ewig S, Papassotiriou J, et al. Inflammatory parameters predict etiologic patterns but do not allow for individual prediction of etiology in patients with CAP-Results from the German competence network CAPNETZ. Resp Res 2009;10:65. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2714042/pdf/1465-9921-10-65.pdf
- Bergin SP, Tsalik EL. Procalcitonin: the right answer but to which question? Clin Infect Dis 2017; 65:191-93. https://academic.oup.com/cid/article-abstract/65/2/191/3605416/Procalcitonin-The-Right-Answer-but-to-Which?redirectedFrom=fulltext