One of the classic clinical dilemmas is determining if a fluid collection (particularly as it relates to fluid in the thoracic cavity) is a transudate or an exudate.
The diagnosis of exudate can be made if any of the following critera are met:
pleural fluid protein/serum protein > .5 or
pleural fluid LDH/serum LDH > .6 or
pleural fluid LDH > 2/3 of the upper normal limit of serum LDH.
Transudates arise largely due to imbalances in oncotic or hydrdostatic pressures in the thoracic area or movement of fluid from the peritoneal and retroperitoneal cavities. Some specific conditions associated with transudates are:
1. Congestive heart failure
3. Hepatic hydrothorax
6. Nephrotic syndrome
7. Constrictive pericarditis
8. Peritoneal dialysis
9. SVC syndrome
10. Trapped lung
Exudates are effusions that occur primarily from lung and pleural inflammation or from lymphatic obstruction of pleural space. Some causes of exudative effusions are:
2. Pulmonary embolism