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 per microliter) and the primary cell types are mononuclear cells: macrophages, lymphocytes and mesothelial 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 | Exudate | |
Main causes | ↑ hydrostatic pressure, ↓ colloid osmotic pressure | Inflammation-Increased vascular permeability |
Appearance | Clear [1] | Cloudy [1] |
Specific gravity | < 1.012 | > 1.020 |
Protein content | < 2.5 g/dL | > 2.9 g/dL [2] |
fluid protein/ serum protein | < 0.5 | > 0.5 [3] |
SAAG = Serum [albumin] - Effusion [albumin] | > 1.2 g/dL | < 1.2 g/dL [4] |
fluid LDH upper limit for serum | < 0.6 or < 2⁄3 | > 0.6 [2] or > 2⁄3 [3] |
Cholesterol content | < 45 mg/dL | > 45 |
Radiodensity on CT scan | 2 to 15 HU [5] | 4 to 33 HU [5] |
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 and thus appear clearer. [6]
Levels of lactate dehydrogenase (LDH) [7] or a Rivalta test can be used to distinguish transudate from exudate.[ citation needed ]
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.[ citation needed ]
The most common causes of pathologic transudate include conditions that:[ citation needed ]
Edema, also spelled oedema, and also known as fluid retention, dropsy and hydropsy, is the build-up of fluid in the body's tissue, a type of swelling. Most commonly, the legs or arms are affected. Symptoms may include skin that feels tight, the area feeling heavy, and joint stiffness. Other symptoms depend on the underlying cause.
Oncotic pressure, or colloid osmotic-pressure, is a type of osmotic pressure induced by the plasma proteins, notably albumin, in a blood vessel's plasma that causes a pull on fluid back into the capillary.
The pleural cavity, or pleural space, is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable lubrication between the membranes, and also to create a pressure gradient.
Ascites is the abnormal build-up of fluid in the abdomen. Technically, it is more than 25 ml of fluid in the peritoneal cavity, although volumes greater than one liter may occur. Symptoms may include increased abdominal size, increased weight, abdominal discomfort, and shortness of breath. Complications can include spontaneous bacterial peritonitis.
Pleurisy, also known as pleuritis, is inflammation of the membranes that surround the lungs and line the chest cavity (pleurae). This can result in a sharp chest pain while breathing. Occasionally the pain may be a constant dull ache. Other symptoms may include shortness of breath, cough, fever, or weight loss, depending on the underlying cause.
A pleural effusion is accumulation of excessive fluid in the pleural space, the potential space that surrounds each lung. Under normal conditions, pleural fluid is secreted by the parietal pleural capillaries at a rate of 0.6 millilitre per kilogram weight per hour, and is cleared by lymphatic absorption leaving behind only 5–15 millilitres of fluid, which helps to maintain a functional vacuum between the parietal and visceral pleurae. Excess fluid within the pleural space can impair inspiration by upsetting the functional vacuum and hydrostatically increasing the resistance against lung expansion, resulting in a fully or partially collapsed lung.
An exudate is a fluid released by an organism through pores or a wound, a process known as exuding or exudation. Exudate is derived from exude 'to ooze' from Latin exsūdāre 'to sweat'.
The Starling principle holds that extracellular fluid movements between blood and tissues are determined by differences in hydrostatic pressure and colloid osmotic pressure between plasma inside microvessels and interstitial fluid outside them. The Starling equation, proposed many years after the death of Starling, describes that relationship in mathematical form and can be applied to many biological and non-biological semipermeable membranes. The classic Starling principle and the equation that describes it have in recent years been revised and extended.
In medicine, Meigs's syndrome, also Meigs syndrome or Demons–Meigs syndrome, is the triad of ascites, pleural effusion, and benign ovarian tumor. Meigs syndrome resolves after the resection of the tumor. Because the transdiaphragmatic lymphatic channels are larger in diameter on the right, the pleural effusion is classically on the right side. The causes of the ascites and pleural effusion are poorly understood. Atypical Meigs syndrome, characterized by a benign pelvic mass with right-sided pleural effusion but without ascites, can also occur. As in typical Meigs syndrome, pleural effusion resolves after removal of the pelvic mass.
A chylothorax is an abnormal accumulation of chyle, a type of lipid-rich lymph, in the pleural space surrounding the lung. The lymphatic vessels of the digestive system normally return lipids absorbed from the small bowel via the thoracic duct, which ascends behind the esophagus to drain into the left brachiocephalic vein. If normal thoracic duct drainage is disrupted, either due to obstruction or rupture, chyle can leak and accumulate within the negative-pressured pleural space. In people on a normal diet, this fluid collection can sometimes be identified by its turbid, milky white appearance, since chyle contains emulsified triglycerides.
Thoracentesis, also known as thoracocentesis, pleural tap, needle thoracostomy, or needle decompression, is an invasive medical procedure to remove fluid or air from the pleural space for diagnostic or therapeutic purposes. A cannula, or hollow needle, is carefully introduced into the thorax, generally after administration of local anesthesia. The procedure was first performed by Morrill Wyman in 1850 and then described by Henry Ingersoll Bowditch in 1852.
A pericardial effusion is an abnormal accumulation of fluid in the pericardial cavity. The pericardium is a two-part membrane surrounding the heart: the outer fibrous connective membrane and an inner two-layered serous membrane. The two layers of the serous membrane enclose the pericardial cavity between them. This pericardial space contains a small amount of pericardial fluid, normally 15-50 mL in volume. The pericardium, specifically the pericardial fluid provides lubrication, maintains the anatomic position of the heart in the chest (levocardia), and also serves as a barrier to protect the heart from infection and inflammation in adjacent tissues and organs.
Hypoalbuminemia is a medical sign in which the level of albumin in the blood is low. This can be due to decreased production in the liver, increased loss in the gastrointestinal tract or kidneys, increased use in the body, or abnormal distribution between body compartments. Patients often present with hypoalbuminemia as a result of another disease process such as malnutrition as a result of severe anorexia nervosa, sepsis, cirrhosis in the liver, nephrotic syndrome in the kidneys, or protein-losing enteropathy in the gastrointestinal tract. One of the roles of albumin is being the major driver of oncotic pressure in the bloodstream and the body. Thus, hypoalbuminemia leads to abnormal distributions of fluids within the body and its compartments. As a result, associated symptoms include edema in the lower legs, ascites in the abdomen, and effusions around internal organs. Laboratory tests aimed at assessing liver function diagnose hypoalbuminemia. Once identified, it is a poor prognostic indicator for patients with a variety of different diseases. Yet, it is only treated in very specific indications in patients with cirrhosis and nephrotic syndrome. Treatment instead focuses on the underlying cause of the hypoalbuminemia. Albumin is an acute negative phase respondent and not a reliable indicator of nutrition status.
The serum-ascites albumin gradient or gap (SAAG) is a calculation used in medicine to help determine the cause of ascites. The SAAG may be a better discriminant than the older method of classifying ascites fluid as a transudate versus exudate.
Malignant pleural effusion is a condition in which cancer causes an abnormal amount of fluid to collect between the thin layers of tissue (pleura) lining the outside of the lung and the wall of the chest cavity. Lung cancer and breast cancer account for about 50-65% of malignant pleural effusions. Other common causes include pleural mesothelioma and lymphoma.
Lactate dehydrogenase (LDH or LD) is an enzyme found in nearly all living cells. LDH catalyzes the conversion of pyruvate to lactate and back, as it converts NAD+ to NADH and back. A dehydrogenase is an enzyme that transfers a hydride from one molecule to another.
Pleural disease occurs in the pleural space, which is the thin fluid-filled area in between the two pulmonary pleurae in the human body. There are several disorders and complications that can occur within the pleural area, and the surrounding tissues in the lung.
Certain diseases can cause excessive accumulations of fluid in areas of the body such as the abdomen (ascites) or the pleural space around the lungs or the pericardial space around the heart. An estimate of the concentration of protein in such fluids can narrow the differential diagnosis and assist the clinician in establishing a diagnosis. For example, fluid accumulations due to congestive heart failure and liver failure (cirrhosis) are typically lower in protein content and are called transudates whereas fluid accumulations due to cancer and tuberculosis are typically higher in protein content and are called exudates. The Rivalta Test is a simple, inexpensive method that can be used in resource-limited settings to differentiate a transudate from an exudate. It is a simple, inexpensive method that does not require special laboratory equipment and can be easily performed in private practice. The test was originally developed by the Italian researcher Rivalta around 1900 and was used to differentiate transudates and exudates in human patients. It is also useful in cats to differentiate between effusions due to feline infectious peritonitis (FIP) and effusions caused by other diseases. Not only the high protein content, but high concentrations of fibrinogen and inflammatory mediators lead to a positive reaction.
The pleurae are the two flattened closed sacs filled with pleural fluid, each ensheathing each lung and lining their surrounding tissues, locally appearing as two opposing layers of serous membrane separating the lungs from the mediastinum, the inside surfaces of the surrounding chest walls and the diaphragm. Although wrapped onto itself resulting in an apparent double layer, each lung is surrounded by a single, continuous pleural membrane.
Hepatic hydrothorax is a rare form of pleural effusion that occurs in people with liver cirrhosis. It is defined as an effusion of over 500 mL in people with liver cirrhosis that is not caused by heart, lung, or pleural disease. It is found in 5–10% of people with liver cirrhosis and 2–3% of people with pleural effusions. In cases of decompensated liver cirrhosis, prevalence rises significantly up to 90%. Over 85% of cases occurring on the right, 13% on the left, and 2% on both. Although it is most common in people with severe ascites, it can also occur in people with mild or no ascites. Symptoms are not specific and mostly involve the respiratory system.