Light's Criteria

Differentiates transudative from exudative pleural effusions using pleural fluid protein, LDH, and serum comparisons.

g/dL

Pleural fluid total protein

g/dL

Serum total protein

U/L

Pleural fluid lactate dehydrogenase

U/L

Serum lactate dehydrogenase (for ULN calculation)

U/L

Upper limit of normal for serum LDH at your lab

References

  1. Light's Criteria - Medscape
  2. New criteria for the differentiation between transudates and exudates - PMC / Journal of Clinical Pathology

Clinical Notes & Warnings

  • Highly sensitive (98%) but less specific (77-83%) for exudates.
  • May misclassify some transudates (especially diuretic-treated CHF) as exudates.
  • Serum-albumin minus pleural-albumin gradient <=1.2 g/dL suggests exudate (useful for diuretic-treated patients).

Light RW et al. 1972. If Light's criteria suggest exudate but clinically suspicious for transudate (especially on diuretics), check serum albumin - pleural albumin gradient.