P-42 Discrimination between tuberculous and malignant pleural effusions with lymphocytic predominance and low ADA levels

Background: Tuberculous pleural effusion (TPE) occasionally shows low levels of pleural fluid adenosine deaminase (ADA), which are commonly found in malignant pleural effusion (MPE). Thus, the differential diagnosis between TPE and MPE with lymphocytic exudate with low ADA levels is challenging in patients who cannot tolerate an invasive pleural biopsy despite negative rapid microbiological or cytological results. Methods: A retrospective study was conducted on TPE and MPE patients with lymphocytic exudate and ADA levels ＜40 U/L. Clinical and laboratory data were compared between the two groups, and diagnostic performance of independent predictive variables for TPE was assessed using receiver-operating characteristics curves. Results: Twenty-seven TPE and 130 MPE patients were finally included. In multivariate analysis, fever, pleural fluid ADA levels ＞28.6 U/L, and pleural fluid carcinoembryonic antigen (CEA) levels ＜4.2 ng/mL were independent predictors for identifying TPE. The presence of any two predictors provided the largest area under the curve (0.921, 95% CI 0.849-0.994) among all the individual and combined parameters, yielding a sensitivity of 89%, a specificity of 95%, a positive predictive value of 80, and a negative predictive value of 98%. Conclusions: TPE should be considered even in patients with low pleural fluid ADA levels under tuberculosis-endemic areas. The combined use of the three parameters including fever, ADA, and CEA, may be useful in discriminating TPE from MPE with similar lymphocytic predominance and low pleural fluid ADA levels.