Role of Adenosine Deaminase (ADA) In Etiological Classification of Exudative Pleural Effusion

Background: Pleural effusion is an abnormal collection of fluid in the pleural space. On the basis of Light's criteria pleural fluid can be classified as an exudate or transudate. An exudate is almost always secondary to a lung pathology. In India the most common cause of exudative pleural effusion is tuberculosis. Diagnosis of tubercular pleural effusion is not easy as conventional methods have a low diagnostic yield in pleural fluid. Adenosine deaminase (ADA) estimation is a simple biochemical test that can be easily done in the clinical laboratory with quickly available results. A cut off value of >40 IU/L for pleural fluid ADA is said to be diagnostic of tuberculosis. We conducted a prospective observational study of 50 patients presenting with exudative pleural effusion in our hospital in order to study the role of ADA along with biochemical and cytological parameters in the etiological classification of exudative pleural effusion. Results: Sensitivity of ADA for tuberculosis at the cut off value of >40 IU/L was found to be 96.88%, specificity was 82.61%, positive predictive value for tuberculosis was 88.5%, negative predictive value for tuberculosis was 95%. Conclusions: We concluded that pleural fluid cytology, Lymphocyte Neutrophil ratio along with serum ADA levels altogether can help in etiological classification of patients with exudative pleural effusion and using a cut off of > 40 U/L for pleural fluid ADA, patients can be classified as tuberculous or non tuberculous with a reasonably high diagnostic accuracy.