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Am Fam Physician. 2020;102(8):online

Clinical Question

How accurate are biomarkers C-reactive protein (CRP), procalcitonin, and leukocytosis in the diagnosis of community-acquired pneumonia (CAP) in adults with respiratory symptoms?

Bottom Line

This review found that the best evidence supports CRP as the most useful and accurate biomarker for diagnosing CAP in adults presenting with lower respiratory tract symptoms. Procalcitonin has a good positive likelihood ratio (LR+) but a minimally useful negative likelihood ratio (LR−). Leukocytosis has only modest accuracy that is minimally clinically useful. (Level of Evidence = 1b)


The investigators searched PubMed and reference lists of pertinent articles for studies that evaluated the accuracy of readily available biomarkers in adult patients who presented with symptoms of acute respiratory infection and those with clinically suspected pneumonia. The authors included studies with at least one biomarker test and an acceptable reference standard (chest radiography or computed tomography) performed on all participants. They did not exclude any studies based on country, year, or language. Two or more individuals independently reviewed potential studies for inclusion and risk of bias using a standard evaluation tool. Discrepancies were resolved through consensus discussion. The authors ended with 14 studies with a total of 6,599 patients. One-half of the studies occurred in the emergency department, and one-half occurred in the primary care setting. Of the 14 studies, eight were scored at low risk of bias, with the remaining six studies considered at moderate risk of bias.

CRP was the most accurate test (less than 1 mg per dL [10 mg per L]; LR− = 0.27, and greater than 2 mg per dL [20 mg per L], 5 mg per dL [50 mg per L], and 10 mg per dL [100 mg per L]; LR+ = 2.08, 3.68, and 5.79, respectively). Procalcitonin had a good LR+ (greater than 0.25 mcg per L and 0.50 mcg per L; LR+ = 5.43 and 8.25, respectively) but a minimally useful LR−. Leukocytosis was only modestly accurate (greater than 9.5 to 10.5; LR+ = 3.15). Based on existing clinical decision rules using signs and symptoms, if the probability of CAP is 25% or less, a CRP of less than 20 mg per L decreases the probability of CAP to less than 10%, making imaging unlikely to be clinically useful and unnecessary.

Study design: Meta-analysis (other)

Funding source: Self-funded or unfunded

Setting: Various (meta-analysis)

Reference: Ebell MH, Bentivegna M, Cai X, et al. Accuracy of biomarkers for the diagnosis of adult community-acquired pneumonia: a meta-analysis. Acad Emerg Med. 2020;27(3):195–206.

POEMs (patient-oriented evidence that matters) are provided by Essential Evidence Plus, a point-of-care clinical decision support system published by Wiley-Blackwell. For more information, see Copyright Wiley-Blackwell. Used with permission.

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This series is coordinated by Natasha J. Pyzocha, DO, contributing editor.

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