Light’s Criteria (for Exudative Pleural Effusions)

Pleural fluid protein

Serum protein

Pleural fluid lactate dehydrogenase (LDH)

IU/L

Serum LDH

IU/L

Upper limit of normal serum LDH
(based on laboratory reference range)

IU/L

Result

Formula

The effusion is exudative if one of the Light’s criteria has been met:

Pleural fluid protein/serum protein ratio >0.5.
Pleural fluid LDH/serum LDH ratio >0.6.
Pleural fluid LDH level >2/3 upper limit of normal LDH level in serum.

Reference

Light RW. Pleural effusion. New England Journal of Medicine. 2002;346(25):1971-1977. doi:10.1056/nejmcp010731