Pleural effusions occur when an abnormal amount of fluid collects in the pleural space between the lungs and chest wall. They are usually caused by underlying conditions that interfere with fluid drainage from the pleural space. Pleural effusions are classified as transudative or exudative based on the fluid characteristics. Transudative effusions are low in protein and cells and are usually caused by conditions that increase hydrostatic pressure or decrease oncotic pressure like heart failure, liver disease, or kidney disease. Exudative effusions are high in protein and occur due to inflammation from infections, cancers, or other diseases that increase capillary permeability. Diagnostic evaluation involves chest imaging and thoracentesis to analyze pleural fluid. Treatment