[The differential diagnosis between pleural exudates and transudates: the value of cholesterol]

The evaluation of a patient with pleural effusion depends on its classification as exudate or transudate. Many criteria have been established but none has a 100% sensitivity and specificity. The aim of the present study was to assess the value of the cholesterol level to differentiate between exudate and transudate and to establish its utility as compared with other differential criteria.

104 patients with pleural effusion of well defined etiology, permitting their classification into 56 exudates and 48 transudates, were evaluated. In all, Light's criteria were established and cholesterol values in pleural effusion and serum were measured and compared.

Using the lactate dehydrogenase level (LDH) in pleural fluid (PF) and the ratios of LDH and proteins in PF and serum, 100% of exudates and 83% of transudates were correctly classified. A cholesterol level of 40 mg/dl or higher best separated exudates and transudates, with a sensitivity of 96% and a specificity of 92% for exudates. A ratio of 0.3 or higher between cholesterol levels in PF and serum was shown to have a high sensitivity (96%) and lower specificity (85%) for exudates. The highest specificity (92%) was achieved when the protein ratio in PF and serum was combined with PF cholesterol.

The cholesterol level in pleural fluid and the ratio between this value and that in serum are highly useful parameters to differentiate between exudates and transudates.