The prevalence and diagnostic significance of eosinophilic pleural effusions: a meta-analysis and systematic review.

BACKGROUND Eosinophilic pleural effusion (EPE) is defined by an eosinophil count of ≥10% in the pleural fluid and often caused by air or blood in the pleural space. The diagnostic significance of EPEs is still a matter of debate. OBJECTIVE The objective of this study was to systematically review the medical literature to evaluate the diagnostic significance of EPEs. METHODS Electronic databases were searched from 1950 to April 2010 to perform a meta-analysis. Data were extracted using standardized forms, and pooled odds ratios with 95% confidence intervals were calculated. A logistic regression analysis was also performed to evaluate the association between the pleural eosinophil counts and the likelihood of underlying causes of EPEs. RESULTS We identified a total of 687 cases of EPE. The most common cause of EPEs was malignancy (26%) followed by idiopathic (25%) and parapneumonic (13%) effusions. The likelihood of malignancy or tuberculosis was somehow lower in EPEs than in non-EPEs, but the differences were not statistically significant. The prevalence of malignancy was significantly lower in the group of patients that required a pathologic confirmation (21 vs. 30%; p = 0.01). The likelihood of malignancy was inversely correlated with the pleural fluid eosinophil counts. The likelihood of idiopathic effusion was significantly higher in EPEs than in non-EPEs. CONCLUSIONS Malignancy was the most common cause of EPEs. EPEs appeared to be a negative predictor of malignancy when a pleural fluid eosinophil count was extremely high. EPEs were more likely to be idiopathic as compared with non-EPEs.