Diagnostic value of tests that discriminate between exudative and transudative pleural effusions

Study objective: To (1) determine appropriate decision thresholds and diagnostic accuracies for pleural fluid (PF) tests that discriminate between exudative and transudative pleural effusions, and (2) evaluate the quality of the primary investigations. Design: Formal meta-analysis of studies that report the diagnostic value of pleural fluid tests. Setting: Data collected from international academic medical centers. Patients: Hospitalized patients undergoing thoracentesis for pleural effusions. Interventions: Primary investigators were requested to transmit original data from patients described in their studies. Measurements and results: Eight primary studies described 1,448 patients with one or more of the following tests: protein (P)-PF, P-PF/serum ratio (R), bilirubin (BILI)-R, lactate dehydrogenase (LDH)-PF, LDH-R, cholesterol (C)-PF, C-R, and albumin gradient. We found that all eight tests had similar diagnostic accuracies when evaluated by receiver operating characteristic (ROC) analysis except for BILI-R, which was less diagnostically accurate. Decision thresholds determined by ROC analysis differed from previously reported values for LDH-PF (>0.45 upper limits of normal) and C-PF (>45 mg/dL). Paired and triplet test combinations tended to have higher diagnostic accuracies compared with individual tests, but examination of the odds ratios with 95% confidence intervals did not identify a clearly superior test combination. Limitations of the primary studies presented a high likelihood of bias affecting their results. Conclusions: Several strategies exist for clinicians in utilizing PF tests to classify effusions as exudates or transudates but accurate interpretations of these test results will require better designed studies.