Comparative evaluation of alkaline phosphatase (ALP) & adenosine deaminase (ADA) in pleural fluid and serum of patients with pleural effusions

Background: High levels of alkaline phosphatase (ALP) have been suggested for the discrimination between exudative and transudative pleural effusions (PE). Objectives: The purpose of this study is to assess the levels of ALP and Adenosine Deaminase (ADA) in the pleural fluid of patients with PE. We also evaluate the usefulness of ALP activity in differentiating transudates from exudates and further in separating tuberculous PE from other causes of exudative effusions (malignant and parapneumonic PE). Materials and methods: A total of 60 patients, admitted to our hospital, having PE due to various etiologies were included in this study. The patients were divided into four groups according to the final diagnosis: 27 malignant, 19 parapneumonic, 8 tuberculous and 6 transudative PE. Results: Both mean pleural fluid ALP and ADA values were significantly higher in transudates compared to exudates (61.04±58.86 vs. 32.67±10.42 U/mL, p=0.012 and 39.81±41.83 vs. 8.22±4.15 U/L, p=0.0004 respectively). Parapneumonic and tuberculous pleural fluid ALP and ADA levels were significantly higher compared to malignant PE respectively. In ROC curve analysis, sensitivity and specificity values were 98.1% and 83.3% respectively for a cut-off value of 9.2 U/L for pleural ADA and 54.7% and 83.3% respectively for a cut-off value of 45 U/mL. Conclusion: Both ADA and ALP showed the same specificity in distinguishing exudative from transudative PE whereas ADA showed greater sensitivity compared to ALP, although both biomarkers were significantly higher in exudates compared to transudates.