Validation of a diagnostic flowchart for tuberculous pleurisy in pleural fluid with high levels of adenosine deaminase

Introduction: Adenosine deaminase (ADA) in pleural fluid is a useful marker for diagnosing tuberculous pleurisy. However, recent studies have reported a lower specificity of pleural fluid ADA levels. We previously developed a diagnostic flowchart for patients with pleural fluid ADA >= 40 U/L, incorporating variables such as pleural fluid lactate dehydrogenase <825 U/L, predominant pleural fluid neutrophils or cell degeneration, and a pleural fluid ADA/total protein ratio <14. This flowchart was effective in distinguishing between tuberculous pleurisy and other diseases. Here, we conducted a validation analysis of this flowchart. Materials and methods: We retrospectively collected data from 458 patients with pleural fluid ADA concentrations >= 40 U/L across eight institutions from January 2019 to December 2023. The diagnostic accuracy rate, sensitivity, and specificity of the diagnostic flowchart were analysed and compared to those in the original study. Results: Eighty-seven patients were diagnosed with tuberculous pleurisy, and 371 patients were diagnosed with other diseases. The diagnostic accuracy, sensitivity, and specificity for diagnosing tuberculous pleurisy were 77.7%, 86.2%, and 75.7%, respectively. Compared with that in the original study, the rate of tuberculous pleurisy was lower (19.0% vs. 44.5%, p < 0.001), but the diagnostic accuracy rates were not significantly different (p = 0.253). On the basis of the findings from this validation study, we have revised the flowchart to enhance its utility. Conclusion: The diagnostic flowchart exhibited high diagnostic accuracy in this validation study, comparable to that in the original study. This validation confirms the effectiveness of the flowchart, even in settings with a low incidence of tuberculosis.