Table 1:

Characteristics of pleural fluid to guide the need for drainage of the pleural space (1), (3)

CharacteristicUncomplicated parapneumonic effusion that may be managed with antibiotics aloneComplicated parapneumonic effusion requiring pleural space drainage*
Pleural fluid volume≤ 50% of hemithorax> 50% of hemithorax
Pleural fluid configurationFree-flowingLoculated
Appearance on thoracentesisClearTurbid or cloudy, or pus (empyema)
pH level≥ 7.20< 7.20
Lactate dehydrogenase level, U/L≤ 1000> 1000
Glucose level, mmol/L≥ 3.4< 3.4
Gram stainingNegativePositive
Aerobic and anaerobic bacterial cultureNegativePositive
  • * Drainage of the pleural space is indicated when 1 or more characteristics of complicated parapneumonic effusion are present.

  • Computed tomography is often required to determine whether pleural fluid is loculated.

  • For pH analysis, the pleural fluid should be collected anaerobically in a heparinized blood gas syringe and transported on ice.