Background: The differentiation of pleural effusions as exudates or transudates is the first step in the diagnosis of pleural effusions. The aim of this study was to evaluate the usefulness of pleural adenosine deaminase (PADA), for separating transudative pleural effusion from exudative pleural effusion.

Materials and Methods: Using light's criteria, after careful evaluation of all relevant clinical and biochemical parameters of pleural fluid and serum, classically effusions were classified to transudative or exudative. The means and standard deviations of PADA, and pleural/serum ADA (P/S ADA) ratio were calculated for transudative and exudative effusions .The best cut-off values for each test were identified by using the receiver operating characteristic (ROC) curve.

Results: We compared PADA levels between transudative and exudative patients with pleural effusion. According to the criteria used, 32 patients were included in the transudate group and 73 patients in the exudate group. Pleural fluid ADA levels were significantly lower in the transudate group than in exudate one (16.21±6.10 U/lit vs. 22.24±7.50 U/lit P<0.001). Also the mean pleural fluid/serum ADA ratio were (P<0.0001) lower in transudates as compared to exudates (0.76±0.32 vs. 0.91±0.26 P=0.021). Using a cut-off point of 14.5 IU/L, the sensitivity and specificity of pleural ADA in the diagnosis of exudates was computed to be 84.7% and 48.3% respectively. At a cut-off point 0.75, pleural fluid/serum ADA ratio was found to have sensitivity and specificity of 73.2% and 65.5%, respectively.

Conclusion: Measuring PADA is suggested as a useful biochemical marker in differentiating between pleural exudates and transudates.