Evaluation of pleural fluid interferon gamma as a diagnostic marker of tuberculous pleural effusion

Abstract

Context: Establishing etiology of pleural effusion is a common diagnostic problem in clinical practice. The most common cause is tuberculosis (TB). Adenosine deaminase (ADA) is one of the biochemical markers commonly used in the etiological diagnosis of tuberculous pleural effusion. In the past decade several studies on pleural fluid interferon gamma (IFN-γ) showed that it is an important diagnostic marker of TB. Aim: To evaluate the role of immunological marker IFN-γ in pleural fluid and to compare with pleural fluid ADA in the diagnosis of tuberculous pleural effusion with reference to pleural biopsy histology and treatment outcome. Materials and Methods: A total of 50 pleural fluid samples with more than 80% lymphocytes were analyzed for IFN-γ by enzyme-linked immunosorbent assay (ELISA) method and the results were compared with pleural fluid ADA. Clinical, radiological, and laboratory evaluation and response to treatment were noted. Among the 50 test samples, 31were from tuberculous pleural effusion, 14 from malignant effusion and five from effusion due to other causes. Results: Pleural fluid levels of IFN-γ and ADA were significantly higher in tuberculous than in nontuberculous pleural effusions. At the cut off value of 3.7 IU/mL for IFN-γ and 40 U/L for ADA it was found to have sensitivity and specificity of 96.77 and 94.73% for IFN-γ and 83.87 and 78.94% for ADA, respectively; differentiating tuberculous from nontuberculous pleural effusions. Conclusion: IFN-γ is more sensitive and specific marker than ADA for differentiating tuberculous from nontuberculous pleural effusions and helps in rapid and efficient diagnosis.