INVESTIGATION OF A PLEURAL EFFUSION

• Take history, clinical examination and chest X-ray

Clinically pleural infection

• See Pleural Infection and Empyema guideline

Clinically transudate

• e.g. LVF, hypoalbuminaemia, dialysis
• Treat underlying cause

Outcome of treatment

• If the effusion has resolved, stop further investigations for pleural effusion
• If the effusion has not resolved, follow exudate/unresolved

Clinically exudate/unresolved

• Refer to respiratory physician
• Pleural aspiration under ultrasound guidance – see Pleural aspiration of fluid guideline
• Send samples for: cytology, protein, LDH, glucose, pH, Gram stain, culture and sensitivity and TB cultures
• take blood at same time for LDH, protein and glucose
• If chylothorax suspected, send samples for cholesterol and triglyceride and for centrifuging
• If haemothorax suspected, send sample for haematocrit
• If rheumatoid disease suspected, send samples for glucose and complement
• If pancreatitis, pancreatic pseudocyst, pregnancy, pleural malignancy or acute rupture of oesophagus suspected, send sample for amylase

Appearance

• If the fluid has a putrid odour, suspect anaerobic empyema
• If the fluid has food particles, suspect oesophageal rupture
• If the fluid is bile stained, suspect chylothorax (biliary fistula)
• If the fluid is milky, suspect chylothorax/pseudochylothorax
• If grossly bloody, consider malignancy, pulmonary infarction, trauma, benign asbestos effusion or post-cardiac injury syndrome
• If in doubt about haemothorax, request haematocrit on pleural fluid:
• if <1%, blood in pleural space is not significant

Biochemistry

• If serum protein is normal and:
• fluid protein >35 g/L, fluid is most likely exudate
• fluid protein <25 g/L, fluid is most likely transudate
• fluid protein between 25 and 35 g/L, use Light’s criteria as below
• Light’s criteria: an exudative effusion is defined when one of the following is present
• pleural fluid protein/serum protein >0.5
• pleural fluid LDH/serum LDH >0.6
• pleural fluid LDH >2/3 x upper limit of normal serum LDH
• Pleural fluid pH
• >7.4 suggests transudative effusion, and virtually rules out tuberculous effusion
• <7.3 suggests exudative effusion
• <7.2 in parapneumonic effusion indicates thick empyema requiring tube drainage
• <7.1 in malignant pleural effusion is a bad prognostic sign (mean survival <6 weeks)
• Pleural fluid glucose <3.3 mmol/L is found in:
• empyema, tuberculosis, malignancy
• rheumatoid disease, SLE
• oesophageal rupture
• Pleural fluid glucose <2 mmol/L or pleural fluid glucose/serum glucose <0.5 mmol/L
• in parapneumonic effusion indicates complicated pleural infection requiring tube drainage
• in malignant pleural effusion is a bad prognostic indicator
• If pleural fluid glucose >1.6 mmol/L or pleural fluid C4 complement >0.04 g/L, effusion unlikely to be caused by rheumatoid disease
• In pancreatitis, pancreatic pseudocyst, pregnancy or pleural malignancy, acute rupture of oesophagus, amylase is high
• higher than upper limit for normal and pleural fluid/serum ratio >1

Cytology

• Positive in only 60% of malignant effusions
• if first specimen negative, refer to respiratory physicians for pleural biopsy
• Pleural lymphocytosis common in malignancy and TB, but not diagnostic
• Pleural eosinophilia not diagnostic

Microbiology and histology in case of possible TB effusion

• Smears for AAFB positive in 10–20% only; cultures positive in 25–50%
• addition of pleural biopsy for TB culture and histology raises diagnostic rate to 90%

Known diagnosis

• If the fluid is a transudate, treat cause
• If the fluid in an exudate, treat appropriately

Still unknown diagnosis

Further investigations

• Request contrast-enhanced CT thorax – see Prevention of contrast-induced acute kidney injury guideline
• Consider pleural biopsy under LA, thoracoscopy, VATS or radiological guidance
• Send biopsy for histology and TB culture together with a repeat pleural aspiration for cytology, microbiology studies +/– special tests
• If symptomatic, drain fluid

Outcome

• If cause found, treat appropriately
• if pleural infection and/or empyema, see Pleural Infection and Empyema guideline
• If no cause found, reconsider thoracoscopy
• if still no cause found, reconsider treatable conditions such as PE, TB, chronic heart failure and lymphoma
• wait and watch as appropriate