JE Heffner, LK Brown, C Barbieri and JM DeLeo
Department of Medicine, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85001, USA.

Controversy exists regarding the clinical utility of pleural fluid pH, lactate dehydrogenase (LDH), and glucose for identifying complicated parapneumonic effusions that require drainage. In this report, we performed a meta-analysis of pertinent studies, using receiver operating characteristic (ROC) techniques, to assess the diagnostic accuracy of these tests, to determine appropriate decision thresholds, and to evaluate the quality of the primary studies. Seven primary studies reporting values for pleural fluid pH (n = 251), LDH (n = 114), or glucose (n = 135) in pneumonia patients were identified. We found that pleural fluid pH had the highest diagnostic accuracy for all patients with parapneumonic effusions as measured by the area under the ROC curve (AUC = 0.92) compared with pleural fluid glucose (AUC = 0.84) or LDH (AUC = 0.82). After excluding patients with purulent effusions, pH (AUC = 0.89) retained the highest diagnostic accuracy. Pleural fluid pH decision thresholds varied between 7.21 and 7.29 depending on cost- prevalence considerations. The quality of the primary studies was the major limitation in determining the value of pleural fluid chemical analysis. We conclude that meta-analysis of the available data refines the application of pleural fluid chemical analysis but a clearer understanding of the usefulness of these tests awaits more rigorous primary investigations.

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