Thoracentesis – What to Measure?

Features to evaluate of a thoracentesis aspirate:

• specific gravity
• WCC and differential
• Protein and Glucose concentrations
• Lactate Dehydrogenase
• pH and pCO2
• amylase
• Gram stain + cultures (+ AFB)
• exfoliative cytology
• ±rheumatoid factor (RF)
• ± complement (C3/C4) levels

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Pearls:

• low pH (< 7.20) – often indicates empyema probably requiring tube drainage
• very low glucose – rheumatoid arthritis
• very high amylase – pancreatitis, ruptured oesophagus

Signs of pleural fluid:

• percussion: very dull
• breath sounds: absent (± bronchial breathing above)
• vocal resonance / fremitus: absent
• added sounds: nil

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Causes of a pleural effusion:

1. carcinoma of the bronchus
2. lobar pneumonia – bilateral
3. pulmonary embolus – bilateral
4. right heart failure – bilateral
5. subdiaphragmatic pathology
   1. cirrhosis
   2. nephrotic syndrome
   3. acute pancreatitis
6. others
   1. rheumatoid arthritis
   2. systemic lupus erythematosus
   3. mesothelioma

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Transudate (< 30 g/L)

• right heart failure
• nephrotic syndrome
• liver failure
• Meig’s syndrome

Exudate (> 30 g/L)

• pneumonia
• neoplasm
  • bronchial carcinoma
  • metastases
  • mesothelioma
• tuberculosis
• pulmonary infarction
• subphrenic abscess
• pancreatitis
• connective tissue diseases
  • rheumatoid arthritis
  • systemic lupus erythematosus