Pleural fluid to serum cholinesterase ratio to discriminate between transudates and exudates: reevaluation in 177 patients

Objective: In a previous study we concluded that the pleural fluid/serum (PF/S) ratio of cholinesterase was the most useful parameter to discriminate between exudates and transudates. The objective of the present study was to confirm these findings in a prospective series of patients with pleural effusion.

Methods: A total of 177 patients, consecutively studied at two institutions, with the diagnosis of pleural effusion were included in this study. Thirty-six (20.3%) effusion were transudates and 141 (79.7%) exudates; of these, 73 and 68 were of malignant and benign origin, respectively. Both PF/S cholinesterase and Light's criteria were compared.

Results: The PF/S cholinesterase ratio incorrectly classified 12 pleural effusions (6.8%). These included 7 out the 36 transudates (19.4%) and 5 out of the 141 exudates (3.5%), the latter of malignant etiology. Following Light's criteria, four (2.2%) exudates were misclassified, all of them transudates. The higher accuracy of Light's criteria was statistically significant (p = 0.04).

Conclusions: In this series of patients, Light's criteria were more accurate than PF/S cholinesterase ratio to discriminate between transudates and exudates. From these results, the use of the PE/S cholinesterase ratio parameters is no longer recommended.