Differential diagnosis of tuberculous and malignant pleurisy using pleural fluid adenosine deaminase and interferon gamma in Taiwan

Accurately differentiating tuberculous pleurisy from lung cancer is important for disease management but difficult using conventional laboratory methods. This study assessed the value of adenosine deaminase (ADA) and interferon gamma (IFN-γ) for differentiating the two conditions in a region of Taiwan with a high prevalence of tuberculosis. The study population comprised patients with lymphocytic exudative pleural effusions: tuberculous (n= 24) and malignant (n= 42). Mean levels of ADA and IFN-γ in pleural fluid, measured with commercial standardized kits, were significantly higher for tuberculous than for malignant pleurisy (p<0.001 for both). For differentiating the two effusions, results for ADA versus IFN-γ were: sensitivity, 70.8% versus 91.7%; specificity, 95.2% versus 97.6%; positive predictive value, 89.5% versus 96.7%; and negative predictive value, 85.1% versus 95.3%. IFN-γ allows precise diagnosis of pleural tuberculosis, but ADA is easier to use, has a low cost, and results are quickly available. Our study confirms previous studies and extends the usefulness of these diagnostic methods to a wider group of clinical laboratories by showing the reliability of standardized relatively inexpensive commercial kits. We recommend that initial ADA screening be used in conjunction with IFN-γ measurements for differential diagnosis of tuberculous pleurisy.