Pleural Fluid is a serous fluid. A serous membrane covering the lung pleura secretes this fluid. The fluid, produced by the parietal circulation, is reabsorbed into the lymph by the lymphatic system. The production and reabsorption is a constant, continuously process. Pleural fluid fills the pleural cavity, the space between 2 pleura: visceral and parietal. A few mL of fluid is always present in this space.
An increase in the amount of fluid, or a pathological buildup of fluid, is referred to as a pleural effusion. This occurs if there is a blockage in the lymphatic system, such as cancer, a tumor, or a lymph node removal, any increase in capillary permeability, changes in vascular pressures (hydrostatic or osmotic), and may be either exudates (high protein content) or transudates (low protein content). Exudates are usually caused by microbial infections, such as bacterial pneumonia, tuberculosis, coccidioides, or by cancers, inflammatory conditions, or collagen vascular diseases. Transudates, on the other hand, are a result of congestive heart failure, nephrotic syndrome, pulmonary embolism, or liver cirrhosis.
When pleural fluid is sent to the laboratory for analysis, it is usually sent to various areas, such as cytology for cell and cytopathic evaluation and to look for cellular changes, microbiology to see if there is a microbial infection, hematology for cell counts and differentials, chemistry for pH and chemical studies, special chemistry to flag any possible tumor markers, and whatever areas needed to diagnose the cause of abnormal accumulation of fluid. When the fluid is received, it is observed for volume, color, clarity, viscosity, gross appearance, and odor.
MACROSCOPIC APPEARANCE:
Clear straw-colored: If transudative, no further analysis needed. If exudative, additional studies needed to determine cause (cytology, culture, biopsy).
Mesothelial cells (if decreased, the patient may have pleuritis)
Inflammatory cells
Neutrophils (pleural empyema)
Lymphocytes (may predominate in TB, and mesothelial cells may be rare)
Eosinophils (may be observed if the pleural tap was recent; usually non-significant)
Malignant cells (cytology and histology studies aid in these findings)
CHEMISTRY:
pH studies
LDH ratio
Specific gravity
Bilirubin
Cholesterol
Pleural fluid-serum protein ratio
Amylase
May be increased in pleural effusions caused by pancreatitis, cancer, esophogeal conditions, or gastrointestinal conditions
Exudates: high protein content
Transudates: low protein content
By National Heart, Lung and Blood Institute - Thoracentesis, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5988160
Pleural fluid from pleural effusion
By BruceBlaus - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44806951
The tools used for thoracentesis: hollow needles to pull out the fluid
Left-sided pleural effusion;By Clinical_Cases: I made the photo myself, licensed under Creative Commons license. - http://en.wikipedia.org/wiki/Image:Left-sided_Pleural_Effusion.jpgoriginally http://clinicalcases.blogspot.com/2004/02/massive-left-sided-pleural-effusion.html, CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=2294191
Another X-ray showing pleural effusion;By User InvictaHOG on en.wikipediaEdited by InvictaHOG, all edits released into public domainCommons upload by Magnus Manske 13:26, 28 April 2006 (UTC) - http://www.cdc.gov/ncidod/dvbid/dengue/slideset/spanish/set1/vi/slide08.htmhttp://www.cdc.gov/ncidod/dvbid/dengue/slideset/spanish/set1/images/pleural-effusion-index.jpgOriginally from en.wikipedia; description page is (was) here, Public Domain, https://commons.wikimedia.org/w/index.php?curid=738253
Another X-ray showing pleural effusion;By James Heilman, MD - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=14634441
Massive pleural effusion (individual has lung cancer);By James Heilman, MD - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4646165
Malignant mesothelioma;By Nephron - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9416972
Pneumonia with abscess;By CT_chest_in_pneumonia_with_abscesses_caverns_and_effusions_d0.jpg: Christaras Aderivative work: Pierpao.lo (listening) - CT_chest_in_pneumonia_with_abscesses_caverns_and_effusions_d0.jpg, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=11666362
Subpleural abscessBy Yale Rosen from USA (Abscess, subpleural) [CC BY-SA 2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons
Abscess of the lung;By Yale Rosen from USA - Lung abscessUploaded by CFCF, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=31127213
Causes of Microbial Pneumonia Associated With Development of Abscesses: