Transudate or exudate? The Light criteria

The fluid is defined as an exudate if at least 1 of the following 3 criteria is met:
  • Ratio of pleural fluid protein to serum protein > 0.5

  • Ratio of pleural fluid lactate dehydrogenase (LDH) to serum LDH > 0.6

  • Pleural fluid LDH more than 2/3 the upper limits of the laboratory normal serum LDH

  • Information from Light et al, reference 7.