Pleural effusion Transudative pleural effusion 2012-06-08T07:31:00Z Transudates result from imbalances in hydrostatic and oncotic forces and are caused by a limited number of recognized clinical conditions such as heart failure and cirrhosis. Less common causes include nephrotic syndrome, atelectasis, peritoneal dialysis, constrictive pericarditis, superior vena caval obstruction, and urinothorax. SNOMEDCT_US:79231000 HP:0011920 A type of pleural effusion with a transudate (extravascular fluid with low protein content and a low specific gravity). 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. UMLS:C0020312