Diagnostic performance of adenosine deaminase activity in pleural fluid in tuberculous pleural effusion and relevant factors: a single-center experience with 1,491 consecutive patients

Adenosine deaminase (ADA) is a widely-used diagnostic test for tuberculous pleural effusion (TPE), but its accuracy, optimal diagnostic threshold and relevant factors are controversial or unclear. We aimed to reassess these diagnostic variables in a large single center series. This retrospective study included 1,491 TPE patients and 597 malignant pleural effusion patients seen between 2012 and 2019. Receiver operating characteristic curve (ROC) and multivariate logistic regression analysis were performed for the diagnostic performance and relevant factors of ADA. The AUC for ADA was 0.952 (95%CI: 0.942—0.961; p = 0.000) in discrimination of TPE from malignant pleural effusion, with an optimal cut-off value of 26.6 IU/L. While levels > 35 IU/L showed high specificity (97.0%), the significant 20–35 IU/L overlap underscores the need for integrated diagnostic approaches in this gray zone. The accuracy of ADA was significantly correlated with age (OR = 0.97; 95% CI: 0.95–0.99; p = 0.0066), pleural monocyte ratio (OR = 1.02; 95% CI: 1.00–1.04; p = 0.0346) and CD45+ relative count (OR = 0.942; 95% CI: 0.90–0.99; p = 0.015). Pleural ADA had good accuracy in the diagnosis of TPE. Age, pleural monocyte ratio and CD45+ relative count may affect pleural fluid ADA accuracy, therefore, ADA results should be interpreted with caution in patients aged > 80 years or with a pleural monocyte ratio < 60%. Moreover, for pleural effusions with ADA 20–35 IU/L, combined diagnostic approaches are superior to fixed cutoffs.