Procalcitonin as a Marker of Etiology in Adults Hospitalized With Community-Acquired Pneumonia

Abstract

Background: Recent trials suggest procalcitonin-based guidelines can reduce antibiotic use for respiratory infections. However, the accuracy of procalcitonin to discriminate between viral and bacterial pneumonia requires further dissection.

Methods: We evaluated the association between serum procalcitonin concentration at hospital admission with pathogens detected in a multicenter prospective surveillance study of adults hospitalized with community-acquired pneumonia. Systematic pathogen testing included cultures, serology, urine antigen tests, and molecular detection. Accuracy of procalcitonin to discriminate between viral and bacterial pathogens was calculated.

Results: Among 1735 patients, pathogens were identified in 645 (37%), including 169 (10%) with typical bacteria, 67 (4%) with atypical bacteria, and 409 (24%) with viruses only. Median procalcitonin concentration was lower with viral pathogens (0.09 ng/mL; interquartile range [IQR], <0.05-0.54 ng/mL) than atypical bacteria (0.20 ng/mL; IQR, <0.05-0.87 ng/mL; P = .05), and typical bacteria (2.5 ng/mL; IQR, 0.29-12.2 ng/mL; P < .01). Procalcitonin discriminated bacterial pathogens, including typical and atypical bacteria, from viral pathogens with an area under the receiver operating characteristic (ROC) curve of 0.73 (95% confidence interval [CI], .69-.77). A procalcitonin threshold of 0.1 ng/mL resulted in 80.9% (95% CI, 75.3%-85.7%) sensitivity and 51.6% (95% CI, 46.6%-56.5%) specificity for identification of any bacterial pathogen. Procalcitonin discriminated between typical bacteria and the combined group of viruses and atypical bacteria with an area under the ROC curve of 0.79 (95% CI, .75-.82).

Conclusions: No procalcitonin threshold perfectly discriminated between viral and bacterial pathogens, but higher procalcitonin strongly correlated with increased probability of bacterial pathogens, particularly typical bacteria.

Keywords: antibiotic stewardship; etiology; pneumonia; procalcitonin.

Figure 1.

Flow diagram of patient participation. Abbreviations: EPIC, Etiology of Pneumonia in the Community; PCT, procalcitonin.

Figure 2.

Box plot of serum procalcitonin (PCT) concentration by pathogen group. The center of each box plot represents the median, with the box denoting the interquartile range (IQR), the whiskers representing 1.5 times the IQR, and dots showing outliers beyond the whiskers. Displayed P values were calculated with the rank-sum test.

Figure 3.

Receiver operating characteristic curves for procalcitonin (PCT) to discriminate bacterial (including typical and atypical bacteria) from viral pneumonia (A), typical bacterial from viral and atypical pneumonia (B), and bacterial (including typical and atypical bacteria) from nonbacterial pneumonia (C). Selected PCT cut-points (0.1 ng/mL, 0.25 ng/mL, 0.5 ng/mL, 1.0 ng/mL) are displayed. Abbreviations: AUC, area under the curve; CI, confidence interval.

Figure 4.

Probability of bacterial (atypical or typical) vs viral detection (A), typical bacterial vs viral or atypical detection (B), and bacterial (typical or atypical) vs no bacterial (including unknown etiology) (C) detection according to serum procalcitonin (PCT) concentration. Shaded areas represent 95% confidence intervals. Dashed lines show the overall prevalence of any bacteria (A and C) or typical bacteria (B) without considering PCT level. The x-axes were truncated at a PCT of 15 ng/mL due to the small number of patients with concentrations above this level.