The closed cavities of the body—namely, the pleural, pericardial, and peritoneal cavities—are each lined by two membranes, visceral membrane and parietal membrane.
There is a small amount of fluid between the membranes that is an ultrafiltrate of plasma. When the production and reabsorption of the ultrafiltrate is not balanced, fluid may accumulate, resulting in effusion. Effusions may be classified as transudate or exudate.
Classifying a serous fluid as transudate or exudate can provide a valuable initial diagnostic step and aid diagnosis of underlying cause. Followings are the differences between transudate and exudate :
|Cause||Usually develop from imbalances in hydrostatic and oncotic forces in circulation.||Usually develop from increased capillary permeability or decreased lymphatic reabsorption.|
|Appearance||Clear, thin-colored, pale yellow||Turbid, hemorrhagic, straw colored|
|Fibrinogen||Low content of fibrinogen (low tendency to clot)||High content of fibrinogen (high tendency to clot)|
|Glucose content||Same as plasma||Low (less than 60 mg/dl)|
|Total Protein||Less than 3 gm/dl||More than 3 gm/dl|
|LDH||<0.67 x UNL Serum||>0.67 x UNL Serum|
|Differential count||Mesothelial cells or lymphocytes||Polymorphs, lymphocytes or RBCs|