The utility of pleural fluid cell IFN-γ production assay in the diagnosis of tuberculous pleurisy

Background: Diagnosis of tuberculous pleurisy is sometimes difficult using conventional diagnostic methods. We have investigated the utility of pleural fluid cell IFN-γ production assay in the diagnosis of tuberculous pleurisy. Methods: We prospectively performed pleural fluid cell IFN-γ production assay in 39 patients with tuberculous pleural effusions (TFE) and in 26 patients with nontuberculous pleural effusions (NTFE) (13 malignant pleural effusions and 13 parapneumonic effusions). Pleural fluid cells were cultured in DMEM media and stimulated with purified protein derivatives (PPD), and phytohemagglutinin (PHA) for 24 hr. The amount of IFN γ released in the culture supernatant was quantitated by IFN-γ ELISA assay. We have also measured adenosine deaminase (ADA) activities and IFN γ concentrations in the pleural fluid. Results: 1) The pleural fluid levels of ADA activity and IFN γ concentrations were significantly higher in TPE than NTPE (p<0.01). 2) IFN γ production in TPE cells stimulated by PPD (755,266±886,636 pg/ml) was significantly higher than NTPE cells (3,509±6,980 pg/ml) (p<0.01). By considering the fact that IFN-γ concentrations over 10,000 pg/ml is a criteria for the diagnosis of TBE, sensitivity and specificity of the test were 97.4 and 92.3%, respectively. 3) The ratios of IFN-γ production by the stimulation with PPD and PHA (PPD/PHA) were significantly higher in TPE cells (59±85) than NTPE cells (5±18)(p<0.01). Considering the criteria for the diagnosis of TBE as PPD/PHA ratio over 5, sensitivity and specificity of the test were 76.9 and 92.3%, respectively. Conclusion: Pleural fluid cell IFN γ production assay may be useful for the diagnosis of tuberculous pleurisy.