In none of the groups of patients was there statistically significant correlation between cholesterol and leukocytes/cu nun in pleural fluid. In the three exudate groups, PCHOL was significantly correlated with scrum cholesterol and the pleural LDI7CHOL ratio was significantly correlated with the serum LDI7 CIIOL ratio (Table 5), but neither correlation held in the transudate group.
Discussion
The first step in determining the etiology of a pleural effusion should be its classification as transudate or exudate, since transudates have few possible causes and do not require resorting to the diagnostic techniques that are necessary to distinguish among the many possible causes of exudates.,h Hitherto, the criteria used to distinguish between transudates and exudates have been based on the biochemical parameters proposed by Light et al, though neither iu our experience nor in others have the results been as satisfactory as those reported by Light et al.
Until lately, the cholesterol content of pleural effusions has only been used, together with the concentrations of other lipid fractions, to distinguish between chylothorax and pseudochvlothorax.

Table 5—Correlation Coefficients between Cholesterol levels (CHOL) and LDIJCHOL Ratio in Pleural Fluid and Serum