Interferon-γ in 388 immunocompromised and immunocompetent patients for diagnosing pleural tuberculosis

The level of interferon-gamma (IFN-gamma) in pleural fluid has been reported to be increased in pleural tuberculosis. Nevertheless, its diagnostic value has not yet been well-established, and immunocompromised patients have not previously been evaluated. The aim of this study was to determine the value of the IFN-gamma level in pleural fluid for diagnosing tuberculous pleurisy in immunocompetent and immunocompromised patients. Three hundred and eighty eight consecutive patients were studied prospectively (73 with tuberculous pleural effusions, including nine with concurrent human immunodeficiency virus (HIV) infection and one after liver transplantation, and 315 with nontuberculous effusions). IFN-gamma was measured by radioimmunoassay. The sensitivity of the test, using a 3.7 U.mL-1 cut-off point, was 0.99 (95% confidence interval (95% CI) 0.93-1.00) and the specificity was 0.98 (95% CI 0.96-1.00). The sensitivity of the test did not differ in HIV-positive and HIV-negative patients. Patients with lymphoma, vasculitis or vascular connective tissue disease did not have abnormal IFN-gamma values. In conclusion, the level of interferon-gamma in pleural fluid is a very good diagnostic marker of tuberculous pleural effusion, even in immunocompromised patients.