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An exudate is a fluid released by an organism through pores or a wound, a process known as exuding or exudation.[1] Exudate is derived from exude 'to ooze'[2] from Latin exsūdāre 'to (ooze out) sweat' (ex- 'out' and sūdāre 'to sweat').[3]
An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. It can be a pus-like or clear fluid. When an injury occurs, leaving skin exposed, it leaks out of the blood vessels and into nearby tissues. The fluid is composed of serum, fibrin, and leukocytes. Exudate may ooze from cuts or from areas of infection or inflammation.[4]
| Transudate vs. exudate | ||
|---|---|---|
| Transudate | Exudate | |
| Main causes | ↑ hydrostatic pressure, ↓ colloid osmotic pressure |
Inflammation-Increased vascular permeability |
| Appearance | Clear[5] | Cloudy[5] |
| Specific gravity | < 1.012 | > 1.020 |
| Protein content | < 2.5 g/dL | > 2.9 g/dL[6] |
| fluid protein/ serum protein |
< 0.5 | > 0.5[7] |
| SAAG = Serum [albumin] - Effusion [albumin] |
> 1.2 g/dL | < 1.2 g/dL[8] |
| fluid LDH upper limit for serum |
< 0.6 or < 2⁄3 | > 0.6[6] or > 2⁄3[7] |
| Cholesterol content | < 45 mg/dL | > 45 |
| Radiodensity on CT scan | 2 to 15 HU[9] | 4 to 33 HU[9] |
Types of exudates: serous, serosanguineous, sanguineous, hemorrhaging and purulent drainage.
There is an important distinction between transudates and exudates. Transudates are caused by disturbances of hydrostatic or colloid osmotic pressure, not by inflammation. They have a low protein content in comparison to exudates. 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. For example, the specific gravity of the transudate is usually less than 1.012 and a protein content of less than 2 g/100 mL (2 g%). Rivalta test may be used to differentiate an exudate from a transudate. It is not clear if there is a distinction in the difference of transudates and exudates in plants.
Plant exudates include saps, gums, latex, and resin. Sometimes nectar is considered an exudate.[12] Plant seeds exudate a variety of molecules into the spermosphere,[13] and roots exudate into the rhizosphere; these exudates include acids, sugars, polysaccharides and ectoenzymes, and collectively account for 40% of root carbon.[14] Exudation of these compounds has various benefits to the plant and to the microorganisms of the rhizosphere.[15][16]
