Evaluation of Transthoracic Ultrasonography in Differentiating Pleural Effusions

Pleural effusion is a highly prevalent pleural space disorder and a fundamental step in its clinical workup is determining whether the fluid is a transudate or an exudate. The standard biochemical tool for this classification is Light's criteria, which requires invasive thoracentesis. Given the procedural risks of thoracentesis and the fact that Light's criteria can misclassify up to 25% of transudates as exudates in patients on diuretic therapy, there is a need to establish the diagnostic value of non-invasive imaging modalities like thoracic ultrasound (TUS).

All enrolled participants will undergo a systematic clinical evaluation and three primary diagnostic assessments:

• Clinical Evaluation:

• Participants will undergo a full medical history assessment (evaluating symptoms, duration, and underlying comorbidities) and a physical examination.
• Baseline blood investigations will be drawn, including complete blood count (CBC), liver and kidney function tests, serum albumin, serum LDH, serum total protein, serum glucose and C-reactive protein (CRP).
• Chest Ultrasound (TUS):

• Imaging will be performed using a high-resolution B-mode ultrasound machine equipped with a convex low-frequency probe (3.5-5 MHz) for deep assessment and a linear high-frequency probe (7.5-12 MHz) for near-field evaluation.
• Patients will be examined in a sitting or semi-recumbent position.
• Evaluated sonographic parameters include the echogenicity of the pleural fluid (anechoic, homogenously echogenic, complex non-septated, complex septated, hyperechoic), the presence and number of septations, pleural thickening, surface irregularity, and fluid volume estimation.
• Reference Standard (Thoracentesis):

• Diagnostic thoracentesis will be performed under ultrasound guidance using a standard aseptic technique.
• Pleural fluid will be analyzed for total protein, LDH, glucose, albumin, and cell count (with additional microbiology or cytology if clinically indicated).
• Simultaneous serum protein, LDH, and albumin will be drawn within 2 hours of the procedure.
• The effusion will be officially classified as an exudate or transudate based on Light's criteria.

Inclusion criteria

• Adult patients aged ≥18 years of either sex
• Clinically and radiologically documented pleural effusion (confirmed by chest X-ray and/or thoracic ultrasound)
• Patients scheduled for diagnostic or therapeutic thoracentesis as part of their standard clinical care
• Ability to provide written informed consent

Exclusion criteria

• Patients with a history of prior pleural interventions, including chemical or surgical pleurodesis or previous chest tube insertion on the affected side
• Patients with absolute contraindications to thoracentesis (e.g., uncorrectable coagulopathy, uncooperative patients, or hemodynamic instability)
• Poor transthoracic ultrasound window preventing adequate evaluation of the pleural space (e.g., due to severe obesity, extensive subcutaneous emphysema, or chest wall deformities)
• Patients with traumatic hemothorax.