ABSTRACT
I. Introduction A transudate can be defined as any fluid that has passed through a membrane or interstice, or exuded through a tissue. By definition, a transudate contains minimal quantities of protein and colloids, or cells. A transudate has protein concentration of ∼1.0 g/dL and a low specific gravity (1.016). A transudative pleural effusion denotes accumulation of an abnormal quantity of a transudate in the pleural space. The formation and the accumulation of a transudate in the pleural space occur when the systemic factors influencing the formation or absorption of pleural fluid are altered (1). This occurs when there is an increase in the hydrostatic pressure or a decrease in the oncotic pressure, or a combination of these two factors. The pleural fluid may originate in the lung, the pleura, or the peritoneal cavity. The permeability of the capillaries to proteins is normal in the area where the fluid forms (2,3). In patients with transudative pleural effusions, the pleural membranes themselves are normal and unaffected by pathologic process. The pleural surface is usually inflamed or involved by the underlying process in exudative pleural effusions. An exudative pleural effusion has high protein content, higher specific gravity, and tends to be cellular and turbid in appearance.
