Pleural effusion

BTS 2023 guidelines on Investigation of the undiagnosed unilateral pleural effusion:https://thorax.bmj.com/content/thoraxjnl/78/11/1143.full.pdf

Key recommendations

1. Imaging & initial evaluation

• Imaging findings of a unilateral pleural effusion should always be interpreted in context (clinical history, pleural fluid characteristics) — i.e., the picture is not enough in isolation. 
• Use image-guided thoracentesis (rather than blind) in suspected unilateral pleural effusion, to reduce procedural complications. (Strong recommendation, by consensus) 
• While imaging is essential, a negative chest CT (or other imaging) does not exclude malignancy. 

2. Pleural fluid sampling – volume, containers, and processing

• In cases where malignancy is suspected, submit 25-50 mL of pleural fluid for cytological analysis (strong consensus). 
• Pleural fluid should be sent in appropriate containers: e.g., for suspected infection send in both plain tubes and blood culture bottles (aerobic & anaerobic) if volume allows. (Strong consensus) 
• Process fluid for both direct smear and “cell block” preparation to maximise cytology yield. 

3. Serum & pleural fluid biomarkers

• Serum NT-proBNP may be considered to support a diagnosis of heart-failure related effusion in unilateral cases, but it is not superior to serum NT-proBNP alone and should not be used routinely. (Conditional) 
• Pleural fluid biomarkers (e.g., tumour markers) should not be used routinely to diagnose secondary pleural malignancy (conditional recommendation). 
• In high prevalence settings for tuberculosis, pleural fluid adenosine-deaminase (ADA) and/or interferon-γ can be considered. In low prevalence populations, ADA may be used as an exclusion test. (Conditional) 
• Pleural fluid ANA may be considered to support a diagnosis of lupus pleuritis (conditional).

4. Pleural biopsy & sampling of the pleura

• When investigation remains inconclusive and suspicion remains (e.g., of malignancy or other pleural disease), thoracoscopic or image-guided pleural biopsy may be used depending on clinical indication and local availability. (Strong recommendation) 
• Blind (non-image‐guided) pleural biopsies should not be used. (Strong consensus) 

5. Good practice points / caveats

• In patients with undiagnosed unilateral pleural effusion, multiple conditions may coexist (e.g., heart failure + malignancy) — biomarkers alone should not be used in isolation. 
• Ensure coordination between ED/acute medicine and respiratory teams (or pleural specialist services) when establishing work-flows for unilateral effusion. 
• The guideline emphasises shared decision-making, patient values and minimising invasive procedures when appropriate.