Characteristics of pleural effusion with a high adenosine deaminase level: a case-control study

Background Increased pleural fluid adenosine deaminase (ADA) is useful for diagnosing tuberculous pleurisy (TB), but high ADA levels are associated with other diseases. In this study, we compare various disease characteristics in patients with high-ADA pleural effusion. Methods We retrospectively collected data for 456 patients with pleural fluid ADA levels of ≥ 40 U/L from January 2012 to October 2021. Cases were classified as TB (n = 203), pleural infection (n = 112), malignant pleural effusion (n = 63), nontuberculous mycobacteria (n = 22), malignant lymphoma (ML) (n = 18), autoimmune diseases (n = 11), and other diseases (n = 27), and data were compared among those diseases. Predictive factors were identified by comparing data for a target disease to those for all other diseases. A diagnostic flowchart for TB was developed based on those factors. Results The most frequent disease was TB, though 60.0% of patients were diagnosed with other diseases. Median ADA levels in patients with TB were 83.1 U/L (interquartile range [IQR] 67.2-104.1), higher than those of patients with pleural infection (median 60.9 [IQR 45.3-108.0], p = 0.004), malignant pleural effusion (median 54.1 [IQR 44.8-66.7], p Conclusion Cases involving high pleural fluid ADA levels should be investigated using several factors to distinguish TB from other diseases.