Diagnostic Accuracy of Thoracic Ultrasonography to Differentiate Transudative From Exudative Pleural Effusion

There are limited data examining the diagnostic accuracy of thoracic ultrasonography (TUS) in distinguishing transudative from exudative pleural effusions.

What is the diagnostic accuracy of TUS in distinguishing transudative from exudative effusions in consecutive patients with pleural effusion?

Consecutive patients who underwent TUS and subsequently a diagnostic thoracentesis with a pleural fluid analysis were identified. TUS images of the pleural effusions were interpreted by previously published criteria. We evaluated the diagnostic performance of TUS findings in predicting a transudative vs exudative pleural effusions and specific pleural diagnoses.

We evaluated 300 consecutive pleural effusions in 285 patients. The pleural effusions were classified as exudative in 229 of 300 cases (76%). TUS showed anechoic effusions in 122 of 300 cases (40%) and complex effusions in 178 of 300 cases (60%). An anechoic appearance on TUS was associated with exudative effusions (68/122; 56%) as compared with transudative effusions (54/122; 44%). The presence of a complex-appearing effusion on TUS was highly predictive of an exudative effusion (positive predictive value of 90%). However, none of the four TUS characteristics were highly specific of a pleural diagnosis.

Thoracic ultrasonography is inadequate to diagnose a transudative pleural effusion reliably. Although the TUS findings of a complex effusion may suggest an exudative pleural effusion, specific pleural diagnoses cannot be predicted confidently.