Pleural effusion Exudative pleural effusion 2012-06-08T07:35:47Z UMLS:C3887491 SNOMEDCT_US:13841000119107 A type of pleural effusion with a exudate (extravascular fluid that has exuded out of a tissue or its capillaries due to injury or inflammation). Pleural effusions can be classified as transudates or exudates based on Light's criteria, which classify an effusion as exudate if one or more of the following are present: (1) the ratio of pleural fluid protein to serum protein is greater than 0.5, (2) the ratio of pleural fluid lactate dehydrogenase (LDH) to serum LDH is greater than 0.6, or (3) the pleural fluid LDH level is greater than two thirds of the upper limit of normal for serum LDH. Transudates result from pneumonia, malignancy, thromboembolism, and other causes. HP:0011921