Quantitative US echogenicity to differentiate exudate from transudate pleural effusion

Background: The echo-texture of pleural effusion (PE) can be determined by ultrasound (US) which gives a clue about its etiology. Echogenic PEs are usually due to exudates while anaechoic PEs can be transudate or exudate. This study aims to determine if quantitative measurement of PE echogenicity can non-invasively differentiate exudative from transudative PEs and to explore its correlation with PE biochemical and cellular content. Methods: The study prospectively recruited patients with PE US greyscale images were transferred to a computer to be analysed by an image analysis software. To control the sonographic window difference between patients, liver echogenicity was measured (using the same US settings image depth, gain, and focus position) and compared to that of PE. Pleural fluid relative echogenicity (PFRE) was calculated as the ratio of the PE echogenicity: liver echogenicity. Results: 54 patients were examined, 25males (46.3%) with mean age 52+15.7, exudates were (59%)). PE was due to malignancy in 17 cases, heart failure 9, liver cirrhosis 8, TB 7, empyema 6, Renal disease 5, inflammation 2. Exudates’ median LDH was 499 [298- 1388], Protein 4.2 [3.9- 4.8], and PFRE 0.51 [0.25 – 0.82].Transudates had a median LDH 74 [69-164], Protein 1.9 [1.5 – 2.8] and PFRE 0.24 [.09-.35]. PFRE significantly correlated with LDH (R 0.392, P=0.004) and serum protein (R 0.316, P=0.021). PFRE predicted PE nature with area under the curve for PFRE of 0.77[95%CI 0.64 -00.89]. A PFRE > 0.32 had a sensitivity of 70% and specificity of 74% to predict an exudate. Conclusion: PFRE can predict the nature of Pleural effusion (Exudates VS Transudates) non-invasively with moderate degree of accuracy.