An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. Its composition varies but generally includes water and the dissolved solutes of the blood, some or all plasma proteins, white blood cells, platelets and (in the case of local vascular damage) red blood cells.

Pus is an example of exudate found in infected wounds that also includes bacteria and high concentrations of white blood cells. Clear blister fluid is an example of an exudate that contains water (and solutes) together with some plasma proteins, but not many blood cells.

There is an important distinction between transudates and exudates. Transudates are caused by disturbances of hydrostatic or colloid osmotic pressure, not by inflammation. Medical distinction between transudates and exudates is through the measurement of the specific gravity of extracted fluid. Specific gravity is used to measure the protein content of the fluid. The higher the specific gravity, the greater the likelihood of capillary permeability changes in relation to body cavities.

Exsudation (Medizin)