Light's criteria

• Facts:
  A pleural effusion is an exudate if:
  
  1) ratio of pleural to serum protein is > 0.5 OR
  
  2) ratio of pleural to serum LDH is > 0.6 OR
  
  3) pleural fluid LDH is more than 2/3rds the upper limit of normal of serum LDH
  
  
• Notes:
  If exudate, must then determine whether complicated parapneumonic effusion or uncomplicated