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.