Unstimulated pleural fluid interferon-gamma for diagnosis of tuberculous pleural effusion: a systematic review and meta-analysis
Objective: Unstimulated interferon-gamma may be a useful pleural fluid biomarker in the diagnosis of tuberculous pleural effusion (TPE). However, the exact threshold of pleural fluid interferon-gamma and its accuracy during routine clinical decision making is not clear. We assessed the performance of pleural fluid interferon-gamma in diagnosing TPE and tried to identify a useful assay threshold. Methods: We queried the PubMed and Embase databases for publications indexed until May 2020 that provided both sensitivity and specificity data on unstimulated pleural fluid interferon-gamma for diagnosis of TPE. A bivariate random effects model was employed to compute summary estimates for diagnostic accuracy parameters, both overall as well as at threshold ranges of <2, 2-5, and >5 IU/mL. Results: We retrieved 2048 citations, of which 67 publications (7153 patients) were assessed in our review. The summary estimates for sensitivity, specificity, and diagnostic odds ratio were 0.93 (95% CI 0.91-0.95), 0.96 (95% CI 0.94-0.97) and 310.72 (95% CI 185.24-521.18) respectively. Increasing interferon-gamma thresholds did not translate into any substantial change in diagnostic performance; however, eight studies using thresholds >5 IU/mL showed poorer diagnostic accuracy estimates as compared to other studies with lower thresholds. None of the prespecified subgroup variables significantly influenced relative diagnostic odds ratio in a multivariate meta-regression model. All publications demonstrated high risk of bias. Conclusion: Unstimulated pleural fluid interferon-gamma level provides excellent accuracy for diagnosing TPE, and has a potential of becoming a first-line test for this purpose.