Pleural effusion

Treatment medications (see Treatment Plan section)

• Diuretics for transudative effusions
• Antibiotics (including anaerobic coverage with metronidazole) for complicated parapneumonic effusions [1]
• tPA/DNase for loculated infected effusions [1]

Caution: Pleural fluid eosinophilia should raise suspicion for drug-induced etiology; a detailed medication history is essential before pursuing extensive diagnostic workup [11]

Transudative (systemic process)

• Congestive heart failure (>80% of transudates)
• Hepatic cirrhosis / hepatic hydrothorax
• Nephrotic syndrome
• Peritoneal dialysis
• Hypoalbuminemia
• Atelectasis, myxedema, SVC obstruction, trapped lung

Exudative (local/inflammatory process)

• Parapneumonic effusion / empyema (most common exudate)
• Malignancy (lung, breast, lymphoma, mesothelioma)
• Pulmonary embolism (can be transudate or exudate)
• Tuberculosis
• Autoimmune (SLE, RA)
• Pancreatitis, esophageal rupture
• Drug-induced
• Chylothorax (thoracic duct injury, lymphoma)
• Post-cardiac injury syndrome (Dressler syndrome)

Cannot-miss diagnoses

• Empyema — delay increases mortality
• Hemothorax — trauma, iatrogenic, coagulopathy
• Esophageal rupture — surgical emergency
• Pulmonary embolism — can present with effusion alone
• Malignancy — especially in unilateral, rapidly recurring effusions

Note: Multiple etiologies may coexist in up to 30% of pleural effusions. [2]

Additional findings

• Asymmetric chest expansion (positive LR 8.1) [13]
• Decreased vocal resonance, egophony at the superior border of the effusion
• Tracheal deviation away from the effusion (massive effusion)
• Pleural friction rub (early or resolving effusion)

Systemic clues: [14]

• JVD, S3 gallop, peripheral edema → heart failure
• Ascites, spider angiomata, jaundice → cirrhosis
• Lymphadenopathy, cachexia → malignancy
• Joint swelling, malar rash → SLE
• Unilateral leg swelling → DVT/PE

Pearl: Physical exam has a lower positive likelihood ratio for detection compared to imaging; POCUS should be used early. [3][15]

Serum labs (send concurrently with pleural fluid)

• CBC with differential, CMP, LDH, total protein, albumin
• NT-proBNP (>1500 pg/mL accurate for cardiac etiology without need for thoracentesis) [2-3]
• Coagulation studies (if thoracentesis planned)
• Blood cultures (if infection suspected)

Routine pleural fluid analysis (when thoracentesis performed): [1]

• Protein and LDH (with concurrent serum levels for Light's criteria)
• Cell count with differential
• Gram stain and culture (inoculate blood culture bottles at bedside)
• Cytology (send 50–60 mL if possible; 60% sensitivity for malignancy)
• pH (collect in ABG syringe; <7.2 = complicated parapneumonic effusion)
• Glucose

Light's Criteria — exudate if any one is met: [1][3]

• Pleural fluid protein / serum protein >0.5
• Pleural fluid LDH / serum LDH >0.6
• Pleural fluid LDH >2/3 upper limit of normal serum LDH

Sensitivity ~98% for exudates; specificity ~72% (25% of transudates misclassified, especially with diuretic use). [2] If heart failure suspected but Light's criteria suggest exudate, check serum-pleural albumin gradient >1.2 g/dL to reclassify as transudate. [2-3]

The following table summarizes additional pleural fluid tests based on clinical suspicion:

Diagnostic scoring

• Light's criteria — cornerstone for transudate vs. exudate differentiation [1]
• Porcel clinical scoring model — score ≥7 identifies cardiac etiology with 92% accuracy when Light's criteria suggest exudate [2]

Point-of-care tests

• Bedside POCUS — real-time assessment of effusion size, complexity, and procedural guidance [3]
• Pleural fluid pH — most accurate predictor for need for chest tube drainage in parapneumonic effusions; pH <7.2 = complicated [7]

Specialty tests

• Pleural ADA (adenosine deaminase): 91% sensitive, 88% specific for TB pleuritis [1]
• Pleural IGRA: 95% sensitive, 96% specific for TB [1]
• Pleural fluid triglycerides >110 mg/dL: Diagnostic for chylothorax [1]
• Pleural fluid cholesterol >250 mg/dL: Pseudochylothorax [1]
• Pleural biopsy (CT-guided or thoracoscopic): Indicated when cytology negative but malignancy or TB suspected; thoracoscopy diagnostic in 90% of cytology-negative malignant effusions [1]

Severity stratification

• Small: Blunting of costophrenic angle only; <10 mm on ultrasound — often observation
• Moderate: Opacification of lower 1/3 of hemithorax
• Large/massive: >1/2 hemithorax; risk of respiratory compromise and hemodynamic effects

Typical presentation: Insidious dyspnea with dullness to percussion; often incidental on imaging [1]

Atypical presentations

• Elderly with empyema may present only with fatigue, weight loss, and failure to thrive [1]
• PE-associated effusion may be small and overlooked
• Hepatic hydrothorax can occur without clinically apparent ascites

Initial stabilization

• Supplemental O₂, positioning (upright), IV access
• Hemodynamic support if tamponade physiology present

Transudative effusions — treat the underlying cause: [2]

• Heart failure: Diuresis (furosemide), sodium/fluid restriction, guideline-directed medical therapy
• Cirrhosis: Diuretics (spironolactone + furosemide), sodium restriction, TIPS if refractory [20]
• Nephrotic syndrome: Diuretics, treat underlying glomerular disease
• Therapeutic thoracentesis for symptomatic relief if refractory; limit to 1–1.5 L per session to avoid re-expansion pulmonary edema

Exudative effusions — etiology-specific: [1]

• Simple parapneumonic: Antibiotics alone; monitor for progression
• Complicated parapneumonic (pH <7.2, glucose <40, positive Gram stain/culture): Chest tube drainage (small-bore 14–16 Fr) + antibiotics with anaerobic coverage (metronidazole) [7][20]
• Empyema (frank pus): Urgent chest tube drainage; consider tPA 10 mg + DNase 5 mg instilled via chest tube if loculated [1][19]
• Failure of medical management: VATS (video-assisted thoracoscopic surgery) for decortication; ~30% of patients may require surgical intervention [1]
• Malignant effusion: Therapeutic thoracentesis for symptom relief; for recurrent effusions, indwelling pleural catheter (IPC) or talc pleurodesis [12][20]
• TB pleuritis: Standard anti-TB therapy

Admission criteria

• Complicated parapneumonic effusion or empyema requiring drainage
• Large effusion with respiratory distress or hemodynamic compromise
• New effusion with suspected malignancy requiring expedited workup
• Effusion in setting of sepsis or hemodynamic instability
• Need for chest tube placement

Observation indications

• Moderate effusion with stable vitals awaiting thoracentesis results
• Heart failure exacerbation with effusion responding to diuresis

Discharge criteria

• Small, asymptomatic transudative effusion with clear etiology (e.g., stable heart failure)
• Simple parapneumonic effusion with reliable follow-up and oral antibiotics
• Post-thoracentesis with no pneumothorax and symptom improvement

Specialist consultation triggers

• Pulmonology/interventional pulmonology: Complicated or loculated effusion, recurrent effusion, need for thoracoscopy or IPC [3]
• Thoracic surgery: Failed medical management, empyema requiring decortication
• Oncology: Confirmed or suspected malignant effusion
• Interventional radiology: Loculated effusion not amenable to bedside drainage

Follow-up timing

• Post-thoracentesis: Repeat CXR within 24 hours (or sooner if symptomatic) to rule out pneumothorax
• Simple parapneumonic effusion on antibiotics: Reassess clinically and with imaging in 1–2 weeks [1]
• Undiagnosed exudative effusion: Follow-up within 1–2 weeks with pulmonology for possible repeat thoracentesis, biopsy, or thoracoscopy
• Malignant effusion: Ongoing palliative management with IPC or pleurodesis planning

Return precautions — instruct patients to return immediately for:

• Worsening shortness of breath or new chest pain
• Fever, chills, or rigors (especially post-procedure)
• Sudden sharp chest pain with dyspnea (pneumothorax)
• Hemoptysis or coughing up blood-tinged sputum
• Lightheadedness, syncope, or signs of hemodynamic compromise

Patient counseling

• Effusions often recur if the underlying cause is not addressed
• Importance of medication adherence (diuretics, antibiotics, anti-TB therapy)
• Smoking cessation if applicable
• Expected recovery: Simple effusions resolve in days to weeks with treatment; complicated effusions may require prolonged drainage and weeks of antibiotics [19]