Background: In the United States, CAP was responsible for nearly 50,000 deaths in 2017. Prompt and accurate diagnosis promotes early treatment and avoids unnecessary antibiotic treatment for nonpneumonia lower respiratory tract infection patients. Diagnosis is based on signs and symptoms, as well as available imaging. Inflammatory markers such as CRP, white blood cell count, and procalcitonin are readily available in the ED and outpatient settings.
Study design: Bivariate meta-analysis.
Setting: A systematic review of literature was done via PubMed search to identify prospective studies evaluating the accuracy of biomarkers in patients with cough or suspected CAP.
Synopsis: Fourteen studies met the criteria to be included in the meta-analysis. Summary receiver operating characteristic (ROC) curves generated reported area under the curve of 0.802 for CRP (95% confidence interval, 0.78-0.85), 0.777 for leukocytosis (95% CI, 0.74-0.81), and 0.771 for procalcitonin (95% CI, 0.74-0.81). The combination of CRP greater than 49.5 mg/L and procalcitonin greater than 0.1 mcg/L had a positive likelihood ratio of 2.24 and a negative likelihood ratio of 0.44.
The study had a some of limitations. The blinding of the person performing the index test to the reference standard and vice versa was not clear. Further, it was unclear if the person interpreting the reference standard was blinded to the index test in five studies and absent in one. Other limitations were inconsistent reporting of abnormal post hoc cutoffs and only two biomarkers being reported in a single study.
Combining a biomarker with signs and symptoms has the potential to improve diagnostic accuracy in the outpatient setting further. CRP was found to be most accurate regardless of the cutoff used; however, further studies without threshold effect will prove beneficial.
Bottom line: CRP is a more accurate and useful biomarker for outpatient CAP diagnosis than procalcitonin or leukocytosis.
Citation: Ebell MH et al. Accuracy of biomarkers for the diagnosis of adult community-acquired pneumonia: A meta-analysis. Acad Emerg Med. 2020;27(3):195-206.
Dr. Castellanos is a hospitalist and assistant professor of medicine at UK HealthCare, Lexington, Ky.