Role of Pleural Fluid Lactate Dehydrogenase to Adenosine Deaminase Ratio in the Etiological Differentiation of Exudative Pleural Effusion

Background: Although pleural fluid adenosine deaminase (ADA) level >70 U/L suggestive tuberculous pleural effusion (TPE). High ADA levels can also be seen in pneumonia, empyema, lymphoma, malignancy, and rheumatoid pleuritis. Elevated pleural fluid lactate dehydrogenase (LDH) is seen in tubercular pleural effusion (TPE), parapneumonic pleural effusion (PPE), and malignant pleural effusion (MPE). Therefore, it is challenging distinguish between TPE, PPE, and MPE based on elevated pleural fluid ADA and LDH levels. In this study, we evaluated the use of pleural fluid LDH/ADA ratio as a new parameter for etiological differentiation of exudative pleural effusions. Materials and Methods: A retrospective hospital-based observational study conducted in GHCCD, Visakhapatnam. A total of 52 patients (TPE – 19, PPE – 16, and MPE – 17) with exudative pleural effusion who fulfilled inclusion criteria were taken into study. Qualitative variables have been described in the form of frequency and percentages. Median and interquartile ranges were used for nonnormal distribution values. Receiver operating curve (ROC) curves with area under the curve (AUC) were calculated. P ≤ 0.05 was considered statistically significant. Results: The mean ADA value for TPE was 75.4 U/L (25–195 U/L), PPE was 59.1 U/L (13–180 U/L), and for MPE was 35.52 U/L (10–75 U/L). The mean LDH value for TPE was 887.8 U/L (139–2213 U/L), PPE was 1128 U/L (334–3110 U/L), and for MPE was 1470 U/L (234–4285 U/L). On ROC analysis, pleural LDH/ADA ratio ≤20.81 diagnose TPE with (sensitivity – 84.2%, specificity – 63.6%) with AUC of 0.758 (95% confidence interval [CI]: 0.619–0.866) (P = 0.0001) whereas LDH/ADA ratio in the diagnosis of PPE was found to be >23.39 (sensitivity – 50%, specificity – 66.7%) with AUC of 0.535 (95% CI: 0.391–0.674) (P = 0.689) and the cutoff LDH/ADA ratio in the diagnosis of MPE was found to be >20.86 (sensitivity – 70.6%, specificity – 68.6%) with AUC of 0.724 (95% CI: 0.583–0.839) (P = 0.007). The cutoff value of the LDH/ADA ratio in PPE does not reach the statistical significant value. Conclusion: Pleural fluid LDH/ADA ratio ≤20.81 U/L is predictive of TPE, and >20.86 U/L is predictive of MPE and the cutoff value of 20.8 U/L can be used for etiological differentiation of pleural effusion.