Use of the Hounsfield unit scale in differentiating transudate and exudate in pleural effusion in the emergency department

Attenuation values in computed tomography (CT) are used as a diagnostic aid in certain clinical conditions. In our study, we investigated the effectiveness of attenuation values, obtained through the noninvasive method of CT, in determining the type of pleural effusions in the emergency department. Patients who presented to the emergency department with a diagnosis of pleural effusion and underwent thoracentesis within 48 hours between January 1, 2023, and January 1, 2024, were included in the study. Exclusion criteria were patients under 18 years of age, those without CT imaging, those presenting due to trauma, those with >48 hours between CT and thoracentesis, patients with chest tubes, a history of thoracic surgery/intervention within the last month, or incomplete data. Attenuation values measured on CT were compared with pleural fluid samples interpreted according to Light criteria. A total of 207 patients were evaluated. The mean age in the exudate group (66.00 ± 15.63) was significantly lower than in the transudate group (72.98 ± 10.38) (P < .001). The prevalence of malignancy was significantly higher in the exudate group (34.0%) compared to the transudate group (4.4%) (P < .001). Heart failure was more common in the transudate group (31.1%) (P = .041). The mean Hounsfield unit (HU) value was 16.64 ± 8.04 in the exudate group and 12.22 ± 7.01 in the transudate group, with a statistically significant difference between the groups (P = .001, 95% confidence interval [CI]: 1.79-7.05). At the cutoff point of 14.2, sensitivity was 62.73%, specificity was 75.00%, and the Youden index reached its highest value at 0.377. The area under the curve was 0.710 (95% CI: 0.626-0.794, P < .001), and the positive predictive value at the 14.2 cutoff point was 90.18%. In conclusion, our study demonstrated that the use of CT attenuation in managing pleural effusions in the emergency department can accurately detect exudative effusions as a noninvasive method. However, HU values should be evaluated alongside clinical parameters, and the varying cutoff values reported in different studies suggest that this method may not be sufficient on its own. In the emergency department setting, the use of the HU scale could improve patient management by avoiding complications associated with invasive procedures like diagnostic thoracentesis.