Light's Criteria

Determine whether a pleural effusion is exudative or transudative

The global unit selector only affects unanswered questions
1.Pleural Fluid Total Protein?
2.Serum Total Protein?
3.Pleural Fluid LDH?
4.Serum LDH?
5.Serum LDH Upper Limit of Normal?
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1. Pleural Fluid Total Protein?

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About this Calculator

Light's Criteria are used to determine whether a pleural effusion is exudative or transudative.

Satisfying any ONE criterium means it is exudative:

  • Pleural Total Protein/Serum Total Protein ratio > 0.5
  • Pleural lactate dehydrogenase/Serum lactate dehydrogenase ratio > 0.6
  • Pleural lactate dehydrogenase level > 2/3 upper limit of the laboratory's reference range of serum lactate dehydrogenase.

Light's criteria are the most sensitive for identifying exudates but have lower specificity than other criteria. This means that some patients may be misidentified as having an exudative pleural effusion when they actually have a transudative pleural effusion.

Therefore, if a patient meets Light's Criteria but has a clinical appearance suggestive of a transudative effusion, Dr. Light recommends a serum albumin − pleural albumin < 1.2 mg/dl, to confirm the effusion is exudative. However, do not use the albumin gradient alone to distinguish transudates from exudates as it will misidentify ~13% of exudates as transudates.


Porcel, J. M., Light, R. W.

Diagnostic approach to pleural effusion in adults.

American Family Physician 2006 April 1, 73 (7): 1211-20

Light, R. W.

Clinical Practice. Pleural effusion.

New England Journal of Medicine 2002 June 20, 346 (25): 1971-7