Serous fluids, Slides of Microbiology

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Serous fluids

Reference Books:

 Urinanalysis and body fluids (Susan King

Strasinger- Marjorie Schaub De Lorenzo) Fifth edition

Formation

Serous fluids are formed as ultrafiltrates of plasma. Under normal conditions, oncotic pressure from serum proteins is the same in the capillaries on both sides of the membrane. Therefore, the hydrostatic pressure in the parietal and visceral capillaries causes fluid to enter between the membranes. The filtration of the plasma ultrafiltrate results in increased oncotic pressure in the capillaries that favors reabsorption of fluid back into the capillaries. This produces a continuous exchange of serous fluid and maintains the normal volume of fluid between the membranes.

Specimen Collection and Handling

 Fluids for laboratory examination are collected by needle aspiration from the respective cavities. These aspiration procedures are referred to as thoracentesis (pleural), pericardiocentesis (pericardial), and paracentesis (peritoneal). Abundant fluid (greater than 100 mL) is usually collected.  An ethylene diamine tetraacetic acid (EDTA) tube is used for cell counts and the differential. Sterile heparinized evacuated tubes are used for microbiology and cytology. Chemistry tests can be run on clotted specimens in plain tubes or on heparinized tubes.

Transudates and Exudates

 A general classification of the cause of an effusion can be accomplished by separating the fluid into the category of transudate or exudate.  Effusions that form because of a systemic disorder that disrupts the balance in the regulation of fluid filtration and reabsorption—such as the changes in hydrostatic pressure created by congestive heart failure or the hypoproteinemia associated with the nephrotic syndrome are called transudates.  Exudates are produced by conditions that directly involve the membranes of the particular cavity, including infections and malignancies.

Laboratory Differentiation of Transudates and Exudates

Correlation of Pleural Fluid Appearance and Disease

 To differentiate between a hemothorax and hemorrhagic exudate, a hematocrit can be run on the fluid. If the blood is from a hemothorax, the fluid hematocrit is more than 50 % of the whole blood hematocrit, because the effusion is actually occurring from the inpouring of blood from the injury. A chronic membrane disease effusion contains both blood and increased pleural fluid, resulting in a much lower hematocrit.  Chylous material contains a high concentration of triglycerides, whereas pseudochylous material has a higher concentration of cholesterol.

Significance of Cells Seen in Pleural Fluid

Significance of Chemical Testing of Pleural Fluid ADA: Adenosine deaminase

Significance of Pericardial Fluid Testing

Peritoneal Fluid

Accumulation of fluid between the peritoneal membranes is called ascites, and the fluid is commonly referred to as ascitic fluid rather than peritoneal fluid. In addition to the causes of transudative effusions discussed previously, hepatic disorders such as cirrhosis are frequent causes o ascitic transudates. Bacterial infections (peritonitis )—often as a result of intestinal perforation or a ruptured appendix—and malignancy are the most frequent causes of exudative fluids