Diagnostic performance of antigen induced IFN-? production in pleural fluid in tuberculous pleurisy

Background: Pleural effusion (PE) is widely found in patients with variety of diseases. Tuberculosis is the major cause of pleural fluid (PF). The etiological diagnosis of tuberculous pleurisy (TP) still remains a serious problem. The aim of this study was to evaluate sensitivity and specificity of antigen-induced level of IFN-γ in PF for the diagnosis of TP in comparison with standard tests. Methods: 76 patients with PE of different etiology were involved in the study: tuberculous (n=21) and non-tuberculous pleurisy (n=55). Pleural fluid samples collected from all patients were stimulated by M. tuberculosis antigens. The pleural levels of IFN-γ were tested by ELISA: at baseline and after antigen stimulation in vitro and the difference was estimated (∆IFN-γ, cut-off value 127.0 pg/ml). The diagnostic efficiencies of ∆ IFN-γ and microbiologic examination of PF (smear, cultures), PCR of PF and skin test were compared. Results: The sensitivity of smear PF, cultures PF, PCR PF and skin test were- 3.45% (95% CI, 0.09%-17.76%); 17.65% (95% CI, 3.80%-43.43%); 50.00% (95% CI, 31.30% - 68.70); 54.84% (95% CI, 36.03%-72.68%)respectively, specificity of the corresponding methods were 100.00% (95% CI, 78.20%-100.00%); 100.00% (95% CI, 91.19%-100.00%);84.85% (95% CI, 68.10% - 94.89); 90.00% (95% CI, 73.47%-97.89%), respectively. The sensitivity of ∆ IFN-γ (90.48% (95% CI, 69.62%-98.83%)) was significantly higher than that of standard laboratory tests. However, the specificity of ∆ IFN-γ (100.0% (95% CI, 93.40%-100.0%)) was similar to that of microbiologic examination and PCR of PF. Conclusion: Assessment of ∆ IFN-γ is more reliable for the diagnosis of tuberculosis pleurisy than standard tests.