Differentiation of Exudates from Transudate Pleural Effusion by Measuring Cholesterol and Bilirubin

Introduction & Differentiating exudates from transudate is the first step in examining pleural effusion. Moreover, it is a guide for determination of pathologic trend of background diseases and differential diagnosis. Although Light’s criteria are considered as standard in differentiating exudates from transudate, in some studies pleural fluid cholesterol, ratio of pleural fluid cholesterol to serum and ratio of pleural fluid bilirubin to serum have been considered. This study was performed to investigate the diagnostic efficacy of cholesterol and bilirubin of pleural fluid in differentiating exudates from transudate pleural effusion. This cross-sectional study was performed in Al-Zahra Hospital, Isfahan in 1384, where 86 cases of pleural effusion were assessed by easy and consecutive sampling method. After differentiation of patients with exudates from transudate pleural effusion, based on light’s criteria, related parameters were measured. Using ROC (Receiver Operative Characteristics) curves, area under the curve was determined following by determination of sensitivity, specificity and positive and negative predictive values. Results were analyzed by MC Nemar test. From 86 studied patients, 59 cases were exudates and 27 cases were transudates. Considering the pleural cholesterol above 43 mg/dl as cut off, a sensitivity of 73.8% and specificity of 92% were obtained for the method. Decreasing the cut off level to 35.5 mg/dl, the sensitivity was increased and reached to 81.4%. Ratio of pleural fluid cholesterol to serum more than 0.3 had a sensitivity of 65%, 88% specificity and 85% efficiency for differentiation of pleural effusion while ratio of pleural fluid bilirubin to serum more than 0.6 had 76.3% sensitivity, 74.1% specificity and 75.6% efficacy. The criterion on 3 g/dl protein had the highest sensitivity and specificity in differentiating exudates from transudate pleural effusion and can be used as the best determinant alone. Also pleural fluid cholesterol more than 35.5 mg/dl has suitable sensitivity and specificity and the combination of pleural fluid protein and cholesterol can be used as the best practical determinant. The criterion of pleural fluid cholesterol to serum ratio more than 0.3 has low sensitivity and with reduction of this ratio to 0.14, its sensitivity increases but its specificity will decrease.