Diagnostic value of pleural fluid lactate dehydrogenase/adenosine deaminase ratio in differentiating parapneumonic effusion from tuberculous pleurisy

Objective The purpose of this study was to determine the diagnostic value of pleural fluid lactate dehydrogenase (LDH)/pleural fluid adenosine deaminase (ADA) ratio in differentiating pleural effusions owing to tuberculous pleurisy (TBP) and parapneumonic effusion (PPE). Patients and methods The data of 272 patients (140 patients with TBP and 132 patients with PPE) between January 2012 and October 2018 were analyzed retrospectively. Demographic data of all patients; concurrent serum glucose, albumin, protein, and LDH values; and pleural fluid pH, glucose, albumin, protein, and ADA results have been reviewed. Results Pleural fluid ADA values were statistically significantly higher in the TBP group than PPE (P<0.001). The median values of pleural fluid LDH/ADA ratio between TBP and PPE groups were 16.10 (12.53) and 32.90 (34.45), respectively, which was found to be significantly lower in TBP group (P<0.001). Pleural fluid LDH/ADA ratio's sensitivity, specificity, positive predictive value, and negative predictive value were 90, 59.85, 70.4, and 84.9%, respectively, in the diagnosis of TBP for values less than 28 (P<0.001). Conclusion The ratio of pleural fluid LDH/ADA determined from routine biochemical analysis predicts TBP at value of 28. Measurement of this parameter may help clinicians distinguish between TBP and PPE.