Pleural Fluid Bilirubin to Serum Bilirubin Ratio, comparison with Light’s Criteria.

Abstract

Introduction: Pleural fluid bilirubin and pleural fluid bilirubin to serum bilirubin ratio evaluation had been reported by several in distinguishing exudative from transudative pleural effusions along with Light’s Criteria. The aim of this study was to assess whether pleural fluid bilirubin to serum bilirubin ratio, was a sensitive marker in classifying the pleural effusion as exudative and transudative and its correlation with Light’s criteria.
 Methods: A cross-sectional, observational study of Pleural fluid bilirubin to serum bilirubin ratio ≥ 0.6 for exudates was taken and compared with Light’s criteria overall and its individual parameters to classify exudative and transudative along with the diagnosis. Statistical analysis was done using SPSS 16, Sensitivity, specificity, Positive predictive value (PPV), Negative predictive value (NPV) and diagnostic accuracy of each tests were calculated.
 Results: By diagnosis on discharge out of 86 samples of pleural effusion, 78(90.69%) were exudative and 8(9.3%) were transudative effusion. Among transudative effusion, 72 were classified correctly and 6 were misclassified by pleural fluid Lactate dehydrogenase (LDH) > 2/3rd of serum LDH criteria and out of 8 transudative, 4 were misclassified as exudative. When the pleural fluid to serum bilirubin ratio ≥0.6 was used to differentiate , it categorized 67 as exudative effusion by pleural fluid LDH > 2/3rd of serum LDH criteria and 11 were misclassified as transudative. This criterion had a sensitivity, specificity, PPV and NPV of 85.53%, 50%, 92.88% and 27.78 % respectively with a significant p value of <0.01. 
 Conclusion: The pleural fluid to serum bilirubin ratio can serve as an alternative easy and cost-effective diagnostic tool in differentiating between exudative and transudative pleural effusion. Though, it misclassified 11 exudative pleural fluids as transudative and 4 transudative as exudative. By taking Light’s criteria as a standard, pleural fluid bilirubin to serum bilirubin ratio ≥0.6 was found to be inferior to the Light’s criteria also in terms of sensitivity, specificity, PPV and NPV. Still the pleural fluid to serum bilirubin ratio can serve as an alternative easy and cost-effective diagnostic tool in differentiating between exudative and transudative pleural effusion in low resource settings.