Which of the following is the most appropriate next step to obtain pleural fluid for analysis in a patient with a new pleural effusion?

• A. Pleural Biopsy
• B. Bronchoscopy
• C. Chest CT
• D. Thoracentesis

Answer: (D)

To analyze a new pleural effusion, obtain pleural fluid with thoracentesis. This procedure provides the actual sample needed for pleural fluid analysis—including tests to classify the effusion as exudate or transudate (Light’s criteria), measure pH and glucose, and perform Gram stain/culture and cytology to look for infection or malignancy. Thoracentesis is diagnostic and can be therapeutic by relieving symptoms. The other options don’t yield pleural fluid: pleural biopsy is reserved when cytology is inconclusive or there's suspicion of TB or malignancy; bronchoscopy examines the airways rather than the pleural space; chest CT is imaging to assess anatomy and the effusion but does not obtain fluid for analysis.