Pleural Fluid Interferon-Gamma (IFN-γ) Measurement as a Diagnostic Tool in Tuberculous Pleurisy

Introduction: Tuberculosis is one of the most common causes of pleural effusion (PE). However, the diagnosis of tuberculous pleurisy still remains difficult. Since M. tuberculosis isolation rates in tuberculous effusions are relatively low the histological and microbiological studies of pleural biopsy samples are usually required to confirm the diagnosis. Several biological markers have been proposed to enhance the effectiveness of diagnosing patients with tuberculous pleurisy. The study was undertaken to evaluate the diagnostic accuracy of pleural fluid IFN-γ concentration in differentiation between tuberculous pleural effusion (TPE) and non-tuberculous pleural effusion (nTPE). Material and methods: 94 patients (50 M and 44 F, mean age 59 ± 18, range 18–95 years) with PE were studied. All subjects underwent diagnostic thoracenthesis and extensive laboratory pleural fluid evaluation. Tuberculous pleural effusion was diagnosed in: (1) patients with positive pleural fluid or pleural biopsy culture and (2) patients with granulomas in the pleural biopsy specimen, after exclusion of other granulomatous diseases. IFN-γ level in pleural fluid was measured with commercially available immunoenzymatic assay (Quantikine Human IFN-γ Immunoassay, R&D Systems, USA). Results: Tuberculous pleural effusion was diagnosed in 28 pts. The non-tuberculous pleural effusion group consisted of 66 pts, including 35 with malignant PE, 20 with parapneumonic effusion or pleural empyema, 5 with pleural transudates due to heart failure, and 6 with miscellaneous causes of PE. The mean concentration of IFN-γ was significantly higher in TPE than in nTPE (614.1 ± 324.5 vs. 15.1 ± 36.0 pg/ml, p < 0.0001). At the cut-off value of 100 pg/ml the sensitivity and specificity of the test were 100% and 98.5% respectively. Conclusions: The pleural fluid concentration of IFN-γ was found to be highly sensitive and specific marker of tuberculous pleurisy.