What is the next best step in evaluating a new pleural effusion?

• A. Thoracentesis
• B. Observation
• C. Bronchoscopy
• D. CT Scan

Answer: (A)

Evaluating a new pleural effusion hinges on obtaining pleural fluid for analysis. Thoracentesis allows direct collection of fluid to assess protein, LDH, pH, and to send samples for cytology, Gram stain, culture, and cell counts. This fluid analysis lets you apply Light’s criteria to distinguish exudates from transudates and to identify infection, malignancy, or inflammatory causes, which directly informs diagnosis and management. Observing the patient without diagnostic data isn’t appropriate when the goal is to determine the cause. Bronchoscopy looks at the airways and doesn’t evaluate pleural fluid. CT scans can be helpful for planning or if the initial workup is nondiagnostic, but they don’t replace the need for diagnostic fluid analysis.