Transudate is extravascular fluid with low protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 content and a low specific gravity

Specific gravity

Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 (< 1.012). It has low nucleated cell counts (less than 500 to 1000 /microlit) and the primary cell types are mononuclear cells: macrophage

Macrophage

Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s, lymphocyte

Lymphocyte

A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

s and mesothelia cells. For instance, an ultrafiltrate of blood plasma

Blood plasma

Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

 is transudate. It results from increased fluid pressures or diminished colloid oncotic forces in the plasma.

In females, transudation is a method of lubrication during sexual arousal

Sexual arousal

Sexual arousal, or sexual excitement, is the arousal of sexual desire, during or in anticipation of sexual activity. Things that precipitate human sexual arousal are called erotic stimuli, or colloquially known as turn-ons. There are many potential stimuli, both physical or mental, which can cause...

.
Levels of lactate dehydrogenase

Lactate dehydrogenase

Lactate dehydrogenase is an enzyme present in a wide variety of organisms, including plants and animals.Lactate dehydrogenases exist in four distinct enzyme classes. Two of them are cytochrome c-dependent enzymes, each acting on either D-lactate or L-lactate...

 (LDH) or a Rivalta test

Rivalta test

Rivalta test is used in order to differentiate a transudate from an exudate.A test tube is filled with distilled water and acetic acid is added. To this mixture one drop of the effusion to be tested is added. If the drop dissipates, the test is negative, indicating a transudate...

 can be used to distinguish transudate from exudate

Exudate

An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. It can apply to plants as well as animals. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as sap or blood...

.

Their main role in nature is to protect elements of the skin

Skin

-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

 and other subcutaneous substances against the contact effects of external climate and the environment and other substances – it also plays a role in integumental

Integumentary system

The integumentary system is the organ system that protects the body from damage, comprising the skin and its appendages...

 hygiene.

Transudate usually appears more clear than exudate.

see also: Light's criteria for pleural effusions.
The most common causes of pathologic transudate include: conditions that increase hydrostatic pressure in vessels, left ventricular heart failure, decrease in colloid oncotic pressure in blood vessels, cirrhosis

Cirrhosis

Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...

 (Cirrhosis leads to hypoalbuminaemia and decreasing of colloid oncotic pressure in plasma that causes edema.), and Nephrotic syndrome

Nephrotic syndrome

Nephrotic syndrome is a nonspecific disorder in which the kidneys are damaged, causing them to leak large amounts of protein from the blood into the urine....

 (also due to hypoalbuminaemia caused by proteinuria

Proteinuria

Proteinuria means the presence of anexcess of serum proteins in the urine. The protein in the urine often causes the urine to become foamy, although foamy urine may also be caused by bilirubin in the urine , retrograde ejaculation, pneumaturia due to a fistula, or drugs such as pyridium.- Causes...

).
Exudate

Exudate

An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. It can apply to plants as well as animals. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as sap or blood...

 – extravascular fluid due to vessel alteration during inflammation (increased permeability, vascular constriction then dilation).