Background Pleural effusion is considered an interesting
clinical problem that is commonly faced by physicians and is
caused by several diseases. The ability of computed
tomography (CT) to differentiate transudate effusion from
exudate effusion is still under research.
Objective The aim of this study was to assess the accuracy of
the CT in diagnosing the nature of the pleural effusion.
Patients and methods In this prospective cross-sectional
analytic study, laboratory biochemistry markers were used to
classify pleural effusion into exudate or transudate based on
Light’s criteria. Chest CT without contrast had been done for
all patients, and CTs were diagnosed by the radiologist.
Measurement of the pleural fluid density was done and shown
using the CT attenuation values [Hounsfield unit (HU)].
Results Of 79 patients with pleural effusion, 60 patients had
exudate effusion and 19 patients had transudate. The mean
attenuation values were significantly higher in exudate
effusion (20.11±7.11 HU) versus transudate effusion (13.8
±4.11 HU), with P value of 0.03. Receiver operating
characteristic curve analysis showed that the cutoff for
exudate effusion was optimal at greater than or equal to 15.33
versus less than 15.33 HU for transudate (area under the
curve=0.57; 95% confidence interval: 0.45–0.68). This point
had 85.71% sensitivity and 46.55% specificity.
Conclusion We reasoned the CT attenuation values of the
pleural fluid may replace the laboratory tests in characterizing
the pleural effusion, either exudate or transudate. However,
there was an overlapping HU values in most effusions. So
correlation of the CT results with the clinical findings is
essential, and further CT studies are highly recommended to
confirm and validate these findings.