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Light's Criteria for Exudative Effusions

Provides Light's Criteria to help determine if pleural fluid is exudative.

Protein Parameters
g/dL
g/dL
LDH Parameters
U/L
U/L
U/L

Advice

A thoracentesis is typically indicated if a clinically significant pleural effusion is present that is radiographically at least 10mm thick.

  • A transudative effusion occurs due to an imbalance between the hydrostatic and oncotic pressure.
  • An exudative effusion, however, represents an alteration of the local factors that then precipitates a pleural fluid accumulation.

Management

  • Perform a diagnostic and therapeutic needle thoracentesis or chest tube drainage of pleural effusion.
  • Obtain pleural fluid and serum studies of protein and LDH.
  • Consider additional pleural fluid studies (cell count, differential, culture, cytology, triglycerides).
  • Determine if pleural fluid is exudative by meeting at least one of Light’s criteria:
    • Pleural fluid protein / Serum protein >0.5
    • Pleural fluid LDH / Serum LDH >0.6
    • Pleural fluid LDH > 2/3 * Serum LDH Upper Limit of Normal
  • Review table 1 below to narrow differential:
Exudative Transudative
Malignancy Heart failure
ARDS Atelectasis
Meigs syndrome CSF leak into pleural space
Pancreatitis Hepatic hydrothorax
Eosinophilic granulomatosis with polyangiitis Hypoalbuminemia
Granulomatosis with polyangiitis Nephrotic syndrome
Lupus Peritoneal dialysis
Lung abscess Urinothorax
Chylothorax
Sarcoidosis
Hypothyroidism

  • Fluid color itself can also assist in suggesting a potential etiology as in table 2:
Fluid Appearance/Odor Necessary Fluid Study Differential
Bloody Hematocrit and RBC count Malignancy, trauma, PE, hemothorax
Cloudy Triglycerides Chylothorax
Putrid odor Gram stain and culture Anaerobic infection

Critical Actions

Proper diagnosis of the underlying etiology is important as the treatments for the numerous exudative and transudative etiologies differ significantly. Typically, exudative effusions require a further investigative workup which may include cytopathology studies, biopsy, or even a thoracotomy. Conversely, transudative effusions usually resolve with treatment of the underlying condition.

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