José M. Porcel, Department of Internal Medicine, Hospital Universitari Arnau de Vilanova, IRBLleida, Universidad de Lleida, Lleida, Spain
Graciela Bagüeste, Pleural Medicine Unit, Department of Internal Medicine, IRBLleida, Lleida, Spain
Marina Pardina, Department of Radiology, Hospital Universitario Arnau de Vilanova. Lleida, Spain
Paula Sancho-Marquina, Pleural Medicine Unit, Department of Internal Medicine, IRBLleida, Lleida, Spain
Silvia Bielsa, Pleural Medicine Unit, Internal Medicine Service, Hospital Universitari Arnau de Vilanova, IRBLleida, Universitat de Lleida, Lleida, Spain

Background and objective: The aim of this study was to evaluate the accuracy of computed tomography (CT) attenuation values in differentiating transudates from exudates; a controversial issue in the literature. Methods: A total of 317 consecutive patients with pleural effusions (PE) who underwent both CT and thoracentesis during their hospitalization period were retrospectively analyzed. CT attenuation values were measured in Hounsfield units (HU) and classification of effusions as transudates or exudates was based on the underlying disease. Results: Median CT attenuation values were significantly higher in 217 patients with exudates than in 100 with transudates (6.43 HU vs. 0.67 HU; p < 0.001), but these differences disappeared in non-contrast CT explorations (3.78 HU vs. −0.38 HU; p = 0.166). At the best cutoff value of ≥ 4 HU, CT identified exudates with a sensitivity of 69%, specificity of 66%, likelihood ratio positive of 2, and likelihood ratio negative of 0.47. Conclusions: CT attenuation values of pleural fluid are not able to confidently discriminate between transudative and exudative PE and, therefore, should not influence the decision to perform a diagnostic thoracentesis.

Keywords: Transudates. Exudates. Computed tomography.