Light’s criteria
Pleural fluid is an exudate if one or more of the following criteria are met:

  • Pleural fluid protein divided by serum protein is >0.5

  • Pleural fluid lactate dehydrogenase (LDH) divided by serum LDH is >0.6

  • Pleural fluid LDH >2/3 the upper limits of laboratory normal value for serum LDH