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Background: Pleural effusion is the abnormal and excess accumulation of serous fluid in the pleural space. A number of biochemical tests are required to differentiate transudative from exudative pleural effusion. Pleural fluid to serum protein ratio, pleural fluid to serum lactate dehydrogenase ratio and pleural fluid to serum bilirubin ratio and serum cholesterol are commonly done to differentiate transudative from exudative pleural effusion. Methods: In this study on 25 patients with pleural effusion, by predefined criteria, these patients were divided into three groups as transudative, tubercular and non tubercular exudative group. All patients were investigated to differentiate transudative from exudative pleural effusion. Apart from routine investigations, biochemical tests of pleural fluid as well as blood were performed. Pleural fluid to serum protein ratio and pleural fluid to serum bilirubin were done in all patients. Results: Pleural fluid to serum protein ratio to differentiate exudative pleural effusion showed sensitivity, specificity, positive predictive value and negative predictive value of 86.66%, 100%,100% and 83.33% respectively. Pleural fluid to serum protein ratio to differentiate transudative pleural effusion showed sensitivity, specificity, positive predictive value and negative predictive value of 100%, 86.66%, 83.33% and 100%. Pleural fluid to serum bilirubin ratio to differentiate exudative pleural effusion showed sensitivity, specificity, positive predictive value and negative predictive value of 100%,85.71%,84.62% and 100% respectively. Pleural fluid to serum bilirubin ratio to differentiate transudative pleural effusion showed sensitivity, specificity, positive predictive value and negative predictive value of 85.71%,100%,84.62% and 84.62% respectively. Conclusion: It is concluded that pleural fluid bilirubin to serum bilirubin is a simple, easy, cost effective and highly useful parameter to distinguish transudative from exudative pleural effusion but it does not tell the etiology of pleural effusion.