Transudate is extravascular fluid with low protein content and a low specific gravity (< 1.012). It has low nucleated cell counts (less than 500 to 1000 /microlit) and the primary cell types are mononuclear cells: macrophages, lymphocytes and mesothelia cells. For instance, an ultrafiltrate of blood plasma is transudate. It results from increased fluid pressures or diminished colloid oncotic forces in the plasma.
Transudate vs. exudate 
|Transudate vs. exudate|
|Main causes||Increased hydrostatic
|Specific gravity||< 1.012||> 1.020|
|Protein content||< 25 g/L||> 29 g/L|
|< 0.5||> 0.5|
with blood albumin
|> 1.2 g/dL||< 1.2 g/dL|
upper limit for serum
|< 0.6 or < ⅔||> 0.6 or > ⅔|
|Cholesterol content||< 45 mg/dL||> 45 mg/dL|
Their main role in nature is to protect elements of the skin and other subcutaneous substances against the contact effects of external climate and the environment and other substances – it also plays a role in integumental hygiene.
Transudate usually appears more clear than exudate as it has low protein content.
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 leads to hypoalbuminaemia and decreasing of colloid oncotic pressure in plasma that causes edema.), and Nephrotic syndrome (also due to hypoalbuminaemia caused by proteinuria).
See also 
Exudate – extravascular fluid due to vessel alteration during inflammation (increased permeability, vascular constriction then dilation). This results in an extracellular fluid of high protein content, with cell debris present and high specific gravity (>1.020).
This is in contrast to transudate where the extracellular fluid is an ultrafiltrate of blood plasma and thus larger molecules such as proteins and cell debris are absent.
- The University of Utah • Spencer S. Eccles Health Sciences Library > WebPath images > "Inflammation".
- Heffner J, Brown L, Barbieri C (1997). "Diagnostic value of tests that discriminate between exudative and transudative pleural effusions. Primary Study Investigators". Chest 111 (4): 970–80. doi:10.1378/chest.111.4.970. PMID 9106577.
- Light R, Macgregor M, Luchsinger P, Ball W (1972). "Pleural effusions: the diagnostic separation of transudates and exudates". Ann Intern Med 77 (4): 507–13. PMID 4642731.
- Roth BJ, O'Meara TF, Gragun WH (1990). "The serum-effusion albumin gradient in the evaluation of pleural effusions". Chest 98 (3): 546–9. doi:10.1378/chest.98.3.546. PMID 2152757.
- "IM Quiz: Pleural Adenocarcinoma".
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