Pulm| Pleural Effusions: Transudate vs Exudate

2.19 Pleural Effusions: Transudate vs Exudate Pulmonary system review for the USMLE Step 1 Exam Pleural effusion is an abnormal accumulation of fluid in the pleural cavity. Pleural effusions can be characterized as either exudative or transudative based on the content of the extra fluid. Exudative effusions have high protein and lactate dehydrogenase content, while transudative effusions have low protein and lactate dehydrogenase content. Pleural exudates are commonly caused by lung infections, lung cancer, and inflammatory diseases. Pleural transudates are caused by increased hydrostatic pressures or decreased oncotic pressure within the lung capillaries that force fluid into the pleural cavity. Transudative effusions are not caused by inflammation, so lactate dehydrogenase content is not expected to be high. Proteins are too big to move between cells, so transudative effusions have low protein content.