Concordant and Discordant Exudates and their Impact on the Accuracy of Light′s Criteria to Diagnose Exudative Pleural Effusions

Abstract Introduction To describe the incidence of discordant exudate effusions, their underlying etiologies and their impact on the accuracy of the Light′s criteria to diagnose exudate effusions. Methods A retrospective review of pleural fluid analysis from a cohort of patients with pleural effusion who underwent thoracentesis. Pleural effusions were defined as exudative based on the Light′s criteria. The effusions were further classified in concordant or discordant exudates. Results From 847 pleural effusion samples, 611 (72.1%) were diagnosed as an exudate and 236 (27.9%) as a transudate. In 10.3% of cases ( n =87), there was discordancy between the final pleural fluid diagnosis and the pleural fluid analysis defined by Light′s criteria. In 281 (33.2%) of the 632 effusions classified as an exudate by Light′s criteria were discordant exudates (52 transudates and 229 exudates). In 182 (65%) of the 281 discordant exudates were found to be protein discordant (37 transudates and 145 exudates), and 99 (35.2%) were LDH discordant (15 transudates and 84 exudates). The positive predicted value and positive likelihood ratio of Light′s criteria for the diagnosis of an exudate effusion decreased from 99.4% and 67.4 respectively when the exudates were concordant to 81.5% and 1.7 respectively if they were discordant. Conclusions In a significant percentage of patients, there is discordancy between the results of the pleural fluid analysis and the final clinical diagnosis. Discordant exudates decrease the accuracy of Light′s criteria to identify exudate pleural effusions, increasing the risk of misclassifying a transudate as an exudate. Concordant exudates almost universally establish the presence of an exudative pleural effusion.