Can Ultrasound Pixel Density Serve as a Non-Invasive Alternative to Thoracentesis in Classifying Pleural Effusions?
DOI:
https://doi.org/10.66984/jsmdc.v12.i01.oa.02Keywords:
Pleural effusion, Thoracentesis, Sensitivity and specificityAbstract
Objective: To determine the diagnostic performance of ultrasound pixel density in differentiating exudative from transudative pleural effusions, using Light’s criteria as the gold standard.
Methodology: This cross-sectional validation study was conducted at the Pulmonology Department of Pak Emirates Military Hospital, Rawalpindi from January to April 2026, after institutional ethical approval. One hundred and ten patients with pleural effusions confirmed by ultrasound and scheduled for diagnostic thoracentesis were enrolled using a non-probability consecutive sampling technique. Written informed consent was obtained from all patients. A curvilinear ultrasound probe (3-5 MHz) was used with standardized depth (8 cm) and gain (60 dB) settings. Three frozen B-mode images were obtained per patient, and pixel density was quantified within a 1 cm² region of interest using ImageJ software. Ultrasonographic pixel density ≥9.5 was classified as exudative. Light’s criteria were applied to pleural fluid biochemistry as the gold standard. Data was analyzed using the Statistical Package for the Social Sciences (SPSS) version 27.0.
Results: Among 110 patients (mean age 42.29±9.09 years; 61.8% males), 66(60%) were classified as having exudative and 44(40%) as having transudative pleural effusion according to Light’s criteria. At the 9.5 cut-off value, pixel density demonstrated a sensitivity of 25.76%, specificity of 95.45%, positive predictive value (PPV) of 89.47%, negative predictive value (NPV) of 46.15%, and an overall diagnostic accuracy of 53.64%. Receiver operating characteristic (ROC) analysis showed an area under the curve (AUC) of 0.75 (p <0.001). Median pixel density was significantly higher in exudative effusions (3.35) compared with transudative effusions (1.50) (p <0.001).
Conclusion: Pixel density on ultrasound at a cut-off value of 9.5 demonstrated high specificity with low sensitivity for differentiating exudative from transudative pleural effusion. The ROC analysis showed fair diagnostic accuracy of ultrasound pixel density. This technique may serve as a useful adjunct in the evaluation of pleural effusion; however, it cannot be used as the only diagnostic test instead of thoracentesis.
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Copyright (c) 2026 Journal of Sharif Medical & Dental College is licensed and distributed under the terms of Creative Commons Attribution-NonCommercial 4.0 International License.
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