The Diagnostic Performance of Pleural Fluid Lactate Dehydrogenase to Adenosine Deaminase Ratio for Classifying Pleural Effusions as Infectious or Non-Infectious.: A Cross- Sectional Study

Diagnostic Utility of Pleural Fluid LDH/ADA Ratio

Abstract

Background: Pleural effusion has diverse infectious and non-infectious causes, and accurate differentiation is essential for appropriate treatment. The pleural fluid LDH/ADA ratio can provide a simple and cost-effective approach for distinguishing infectious from non-infectious pleural effusions. Objective: To determine the diagnostic performance of the pleural fluid lactate dehydrogenase to adenosine deaminase ratio for differentiating pleural effusions as infectious or non-infectious. Study Design: Analytical cross-sectional diagnostic study. Settings: Pulmonology Department, Sahiwal Teaching Hospital, Sahiwal Pakistan. Duration: Six months from May 2025 to October 2025. Methods: Patients with pleural effusion were recruited by using a non-probability consecutive sampling technique. Adult patients with radiologically confirmed pleural effusion and pleural fluid adenosine deaminase levels >33 U/L were included. Infectious pleural effusions comprised tuberculous pleural effusion, parapneumonic pleural effusion and empyema, while non-infectious pleural effusions included malignant and transudative pleural effusions. After measuring pleural fluid lactate dehydrogenase and adenosine deaminase levels, the LDH/ADA ratio was calculated. The diagnostic performance of the study biomarkers was assessed using receiver operating characteristic (ROC) curve analysis. Results: The study cohort comprised 170 patients, with 128 (75.3%) classified as having infectious and 42 (24.7%) as non-infectious pleural effusions. Infectious pleural effusions showed significantly higher pleural fluid lactate dehydrogenase, adenosine deaminase, and LDH/ADA ratio values, whereas pleural fluid pH and glucose levels were significantly lower. The LDH/ADA ratio demonstrated the strongest factor independently associated with infectious pleural effusion, with high sensitivity, specificity, and overall diagnostic accuracy. An LDH/ADA ratio >10 was identified as the strongest independent predictor of infectious pleural effusion. Conclusion: The pleural fluid LDH/ADA ratio is a simple, inexpensive and potentially useful biomarker for differentiating infectious from non-infectious pleural effusions and has potential utility as a clinically applicable diagnostic biomarker.