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Light's Criteria

Lighthouse
Picmonic
Light's Criteria is a diagnostic tool used to determine of the cause of a pulmonary effusion; transudate versus exudate. This relies on a comparison of the chemistries in the pleural fluid to those in the blood. According to Light's criteria, a pleural effusion is likely exudative if at least one of the following exists: The ratio of pleural fluid protein to serum protein is greater than 0.5, the ratio of pleural fluid LDH and serum LDH is greater than 0.6, or the pleural fluid LDH is greater than 0.6 or 2⁄3 times the normal upper limit for serum.
4 KEY FACTS
USE
Determines Transudative vs. Exudative Source of Pleural Effusion
Transparent-transudate vs. Oozing-exudate Source of Fluid around Lungs

Light's criteria is used to determine whether the source of a pleural effusion is transudative or exudative.

EXUDATE IF (AT LEAST ONE OF THE FOLLOWING):
Effusion/Serum Protein Ratio > 0.5
Protein-ribbon Above (0.5) Hand

If the ratio of pleural fluid protein to serum protein is greater than 0.5, the effusion fluid is exudative.

Effusion/Serum LDH Ratio > 0.6
Lady-Horns Above (0.6) Horn

The pleural effusion is likely exudative if the ratio of pleural fluid LDH and serum LDH is greater than 0.6

Effusion LDH > Two-thirds Upper Serum LDH Range
Two-thirds Upper Limit with Lady-Horns

If the pleural fluid LDH is greater than 0.6 or 2⁄3 times the normal upper limit for serum, it is likely to be exudative, based on Light's criteria. Different laboratories have different values for the upper limit of serum LDH, but examples include 200 and 300 IU/l.

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