Diagnostic significance of interferon-γ in tuberculous pleural effusions

Study objectives: Tuberculosis (TB), the single most frequent infectious cause of death worldwide, also is a major cause of pleural effusion, which in TB usually has lymphocytic and exudative characteristics. Differential diagnosis between TB and nontuberculous pleural effusion can be sometimes difficult, representing a critically important clinical problem. Methods: We studied 46 patients presenting with pleural effusion to the National Sanyo Hospital between April 2000 and January 2001 (34 men and 12 women; mean age, 64 years). Ten patients (22%) had tuberculous pleurisy, 19 patients (41%) had malignant pleuritis, and 17 patients (37%) had pleural effusion due to an etiology other than tuberculosis or cancer. Pleural fluid concentrations of four suggested markers were measured using commercially available kits. Results: The pleural fluid levels (mean+/-SE) of adenosine deaminase (83.3+/-18.2 U/L vs 25.8+/-20.4 U/L, p<0.0001), interferon-γ (137±230 IU/mL vs 0.41±0.05 IU/mL, p<0.0001), immunosuppressive acidic protein (741+/-213 mug/mL vs 445+/-180 mug/mL, p<0.001) and soluble interleukin 2 receptor (7,618±3,662 U/mL vs 2,222±1,027 U/mL, p<0.0001) were significantly higher for tuberculous pleuritis than for other causes of effusion. Receiver operating characteristic analysis demonstrated that pleural fluid content INF-gamma was the best indicator of tuberculous pleurisy among four relevant biological markers. Conclusions: INF-gamma in pleural fluid is the most sensitive and specific among four biological markers for tuberculous pleuritis. Thus, our results suggest that determination of INF-gamma at the onset of pleural effusion is informative for the diagnosis of tuberculous pleuritis. Further studies including larger numbers of patients are needed to verify this result.