Pleural effusion is a condition where excess fluid builds up in the space between the lungs and the chest wall. To properly treat this condition, doctors must determine if the fluid is a "transudate" (usually resulting from systemic conditions like heart failure or liver disease) or an "exudate" (often resulting from local issues like infections, inflammation, or cancer). The standard method to classify this fluid involves inserting a needle into the chest to draw out a sample for laboratory testing, a procedure known as thoracentesis.

While laboratory fluid analysis is highly accurate, the needle procedure carries some inherent procedural risks. This observational study aims to evaluate whether non-invasive imaging tests, specifically chest ultrasound, can accurately determine if the fluid is a transudate or an exudate.

Researchers will enroll adult patients presenting with pleural effusion at Assiut University Hospital. As part of their diagnostic workup, participants will undergo a chest ultrasound and a standard diagnostic thoracentesis (fluid draw) within 24 to 48 hours of each other. The study will then evaluate the features seen on the ultrasound against the laboratory fluid analysis (the current gold standard) to see how well the non-invasive imaging performs in identifying the specific type of pleural effusion.

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:

1. 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).

2. 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.

3. 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.

The study population comprises adult patients (18 years or older) of both sexes presenting with a clinically and radiologically confirmed pleural effusion (unilateral or bilateral). Participants will be recruited from patients admitted to the Chest Medicine Department or referred for imaging at Assiut University Hospital. Eligible participants are those scheduled to undergo diagnostic thoracentesis and ultrasound of the chest as part of their standard clinical diagnostic workup.