The pleural fluid lactate dehydrogenase/adenosine deaminase ratio differentiates between tuberculous and parapneumonic pleural effusions

Background Although pleural fluid lactate dehydrogenase (LDH) and adenosine deaminase (ADA) levels are often used to distinguish between tuberculous pleural effusion (TPE) and parapneumonic pleural effusion (PPE), this can be challenging as the LDH level may vary from normal to severely increased in PPE and a significantly elevated ADA is frequently measured in both conditions. In this study, we evaluated use of the pleural fluid LDH/ADA ratio as a new parameter to discriminate TPE from PPE. Methods A retrospective study was conducted in patients with pathologically-confirmed TPE (n = 72) and PPE (n = 47) to compare pleural fluid LDH and ADA levels and LDH/ADA ratios between the 2 groups. A receiver operating characteristic (ROC) curve was constructed for identifying TPE. Results The median pleural fluid LDH and ADA levels and LDH/ADA ratios in the TPE and PPE groups were: 364.5 U/L vs 4037 U/L (P