Increased oxidative stress in exudative pleural effusions - A new marker for the differentiation between exudates and transudates?

Study objectives: Oxidative stress has been associated with various respiratory disorders. We tested the hypothesis that exudates would present higher levels of oxidative stress compared to transudates, expressing the increased local oxidative burst in the former. Design: Prospective, cross-sectional study. Patients or participants: One hundred six consecutive patients who had undergone thoracentesis were studied. Ninety patients with a final diagnosis of pleural effusion were further analyzed. Setting: The respiratory department and a clinical laboratory of a tertiary hospital. Interventions: Subjects underwent diagnostic thoracentesis, and standard biochemical parameters (ie, total protein, lactate dehydrogenase, and albumin levels) were measured in pleural fluid and serum. Oxidative stress levels were assessed with a commercially available method (d-ROMs test; Diacron; Grosseto, Italy) that uses conventional Carratelli units (UCarr). In 14 patients, duplicate measurements of oxidative stress and a second thoracentesis were performed on the following day for the assessment of the repeatability of measurements. Receiver operating characteristic (ROC) analysis was performed in order to determine the optimal cutoff level for the differentiation behveen exudates and transudates. Measurements and results: Oxidative stress levels were higher in exudates compared to transudates (mean [+/- SD] stress level, 274 +/- 72 vs 126 +/- 34 UCarr, respectively; p < 0.0001). No significant differences were found among the levels of oxidative stress in exudative effusions of different etiologies. The area under the ROC curve was 0.992 (95% confidence interval, 0.945 to 0.997), and the method provided high sensitivity (96.8%), high specificity (96.3%), and high accuracy (96.7%) for the diagnosis of exudates at a cutoff level for oxidative stress of 186 UCarr. Consecutive measurements of oxidative stress in the same samples and on fluid from two different thoracenteses performed on 2 consecutive days presented excellent repeatability. Conclusions: Oxidative stress levels are higher in exudative pleural effusions compared to transudative effusions, probably due to reactive oxygen species produced in the former.