- Last Update On : 2012-12-31
The serous body cavities are mesothelial lined potential spaces surrounding the lungs, heart and abdomen. Normally, they contain a small amount of fluid that is an ultrafiltrate of plasma. When production and resorption of this ultrafiltrate are not balanced, fluid may accumulate, resulting in an effusion. Effusions may be classified as transudates or exudates. Transudates are usually bilateral and arise from either increased capillary hydrostatic pressure or decreased oncotic pressure secondary to congestive heart failure, fluid overload, cirrhosis or hypoalbuminemia. Exudates are usually unilateral and result from increased capillary permeability or decreased lymphatic resorption associated with infection, autoimmune disease, pancreatitis or cancer.
Several laboratory tests are helpful in distinguishing transudates from exudates including pH, total protein, lactate dehydrogenase (LD), amylase, glucose, white cell count and differential. Only one of these values has to fall