Sputum Color as a Marker for Bacteria in Acute Exacerbations of Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-analysis

Abstract Rationale Diagnosing bacterial infection as the etiology in acute exacerbations of chronic obstructive pulmonary disease (AECOPDs) remains challenging. Sputum discoloration is easily measured and often used as a marker of bacterial infection in AECOPD, although high-quality evidence for this practice is lacking. Objectives To determine the diagnostic accuracy of sputum color as a marker for bacteria in AECOPD. Methods Articles were searched for in electronic databases, and the gray literature were reviewed. Quality assessment of included articles was performed using the revised Quality Assessment of Diagnostic Accuracy Studies tool. A meta-analysis was conducted using a bivariate logistic regression model with random effects. Analysis was conducted on individual sputum samples rather than on individual participants so that each sample represented a unique index test. Results Of the 1,600 candidate studies, 13 eligible studies satisfied the inclusion criteria. These included prospective cohort studies (n = 3), cross-sectional studies (n = 3), and secondary analyses of randomized controlled trials (n = 7). The included studies were all from Europe and North America. Most studies scored high risk of bias in at least one domain. In total, this systematic review and meta-analysis included 5,770 sputum samples. The estimated pooled sensitivity and specificity were 81% (95% confidence interval [CI], 70–88%) and 50% (95% CI, 35–65%), respectively, and these results were not significantly altered in a series of sensitivity analyses. Conclusions Sputum color has limited value as a stand-alone test in diagnosing bacterial infection as the etiology in AECOPD because of its moderate sensitivity and poor specificity.