If any of the following conditions are met, it is an exudate, full of protein and turbid, unclear fluid. Think malignancy or certain infections.

Light’s Criteria

1. Pleural fluid protein / serum protein > 0.5
2. Pleural fluid LDH / serum LDH > 0.6
3. Pleural fluid LDH > 2/3 x upper limit of normal serum LDH

Memory Aid

• Pleural
  • Criterion 1 = protein
  • Criterion 2 = LDH
  • Criterion 3 = LDH again
• Increasing numbers
  • 0.5
  • 0.6
  • 0.666666 to infinity

References

1. MDCalc. (2018). Light’s Criteria for Exudative Effusions. [online] Available at: https://www.mdcalc.com/lights-criteria-exudative-effusions [Accessed 14 Sep. 2018].
2. Exeter Clinical Laboratory International. (2018). Transudate or Exudate / Blood Sciences Test. [online] Available at: https://www.exeterlaboratory.com/test/transudate-or-exudate/ [Accessed 14 Sep. 2018].