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

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.