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 μg/mL vs 445 ± 180 μg/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-γ was the best indicator of tuberculous pleurisy among four relevant biological markers.
Conclusions: INF-γ in pleural fluid is the most sensitive and specific among four biological markers for tuberculous pleuritis. Thus, our results suggest that determination of INF-γ 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.