Background : Cholesterol and lipoprotein level of pleural fluid and their correlation with serum level is of utmost importance in differentiating exudative form transudative pleural fluid. The present study was conducted in patients with pleural fluid referring to Shaheed Beheshti hospital in Kashan during a two-year period.

Materials and methods : It was a cross sectional study. Light's criteria were used to differentiate exudative and transudative pleural fluid. Cholesterol and lipoprotein levels of pleural fluid and serum were determined using the standard techniques and their correlation was calculated by Pearson method. T-test and Mann-Whitney were used for data analysis.

Results : The study population included 52 males and 67 females with the mean age of 63.5±15 years. Pleural effusion was exudative in 70 (58.8%) patients and transudative in 49 (41.2%). Pleural fluid cholesterol level were 29±16 and 65±25 in transudative and exudative group, respectively (p<0.001). Pleural fluid cholesterol level (transudative and exudative) depends on their serum level as well as the ratio of pleural fluid to serum protein (for exudative r=0.61, p<0.001, and for transudative r=0.62, p<0.001). Correlation coefficient of LDL, HDL, VLDL, and triglyceride of exudative pleural fluid with the ratio of pleural fluid to serum protein were 0.53 (p<0.001), 0.40 (p=0.01), 0.29 (p=0.01), and 0.29 (p=0.02), respectively. These figures were 0.48 (p<0.001), 0.24 (p=0.09), 0.09 (p=0.52) and 0.04 (p=0.79) respectively for transudative pleural fluid. The percentage of cholesterol associated with LDL and HDL in exudative and transudative pleural fluid were 90 and 89, whereas their serum percentage were 83 and 86.

Conclusion : Pleural fluid cholesterol level (transudative and exudative) depends on their serum level as well as the ratio of pleural fluid to serum protein. With respect to the unchanged level of pleural fluid lipoproteins, determination of pleural fluid cholesterol level may help us to differentiate exudative from transudative pleural fluid. In exudative pleural effusion the pleural fluid lipoprotein level depends mainly on the ratio of pleural fluid to serum protein, however, in transudative state LDL level depends on this ratio.