At a Glance
Why Get Tested?
When to Get Tested?
When a doctor suspects that someone with chest pain, coughing, and/or difficulty breathing has a condition associated with pleuritis and/or pleural effusion
A volume of pleural fluid collected using a procedure called thoracentesis
Test Preparation Needed?
The Test Sample
What is being tested?
Pleural fluid is found in the pleural cavity and serves as a lubricant for the movement of the lungs during inhalation and exhalation. It is derived from a plasma filtrate from blood capillaries in the lungs and is found in small quantities between the layers of the pleurae – membranes that cover the chest cavity and the outside of each lung.
A variety of conditions and diseases can cause inflammation of the pleurae (pleuritis) and/or excessive accumulation of pleural fluid (pleural effusion). Pleural fluid analysis is a group of tests that evaluate this liquid to determine the cause of the increased fluid.
The two main reasons for fluid accumulation in the pleural space are:
- An imbalance between the pressure of the liquid within blood vessels—which drives fluid out of blood vessels—and the amount of protein in blood—which keeps fluid in blood vessels. The fluid that accumulates in this case is called a transudate. This type of fluid usually involves both lungs and is most frequently a result of either congestive heart failure or cirrhosis.
- An injury to or inflammation of the pleurae, in which case the fluid that accumulates is called an exudate. It usually involves one lung and may be seen in infections (pneumonia, tuberculosis, sarcoidosis), malignancies (lung cancer, metastatic cancer, lymphoma, mesothelioma), or autoimmune disease.
Differentiation between the types of fluid is important because it helps diagnose the specific disease or condition. Doctors and laboratorians use an initial set of tests (cell count, protein, albumin, or lactate dehydrogenase (LDH) level, and appearance of the fluid) to distinguish between transudates and exudates. Once the fluid is determined to be one or the other, additional tests may be performed to further pinpoint the disease or condition causing pleuritis and/or pleural effusion.
How is the sample collected for testing?
A sample of pleural fluid is collected by a doctor with a syringe and needle using a procedure called thoracentesis.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
Ask a Laboratory Scientist
Form temporarily unavailable
Due to a dramatic increase in the number of questions submitted to the volunteer laboratory scientists who respond to our users, we have had to limit the number of questions that can be submitted each day. Unfortunately, we have reached that limit today and are unable to accept your inquiry now. We understand that your questions are vital to your health and peace of mind, and recommend instead that you speak with your doctor or another healthcare professional. We apologize for this inconvenience.
This was not an easy step for us to take, as the volunteers on the response team are dedicated to the work they do and are often inspired by the help they can provide. We are actively seeking to expand our capability so that we can again accept and answer all user questions. We will accept and respond to the same limited number of questions tomorrow, but expect to resume the service, 24/7, as soon as possible.
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Rubins, J. and Mosenifar, Z. (Updated 2012 May 21). Pleural Effusion. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/299959-overview through http://emedicine.medscape.com. Accessed June 2012.
Blaivas, A. (2011 December 15). Pleural fluid analysis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003624.htm. Accessed June 2012.
Light, R. (Revised 2012 May). Pleural Effusion. Merck Manual for Healthcare Professionals [On-line information]. Available online through http://www.merckmanuals.com. Accessed June 2012.
(2011 September 21). How Are Pleurisy and Other Pleural Disorders Diagnosed? National Heart Lung and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/health-topics/topics/pleurisy/diagnosis.html through http://www.nhlbi.nih.gov. Accessed June 2012.
Crawford Mechem, C. (Updated 2011 July 8). Emergent Management of Pleural Effusion. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/807375-overview through http://emedicine.medscape.com. Accessed June 2012.
Rodriguez-Panadero, F. and Romero-Romero, B. (2011 August 31). Management of Malignant Pleural Effusions. Medscape News from Curr Opin Pulm Med. 2011;17(4):269-273 http://www.medscape.com/viewarticle/745553 through http://www.medscape.com. Accessed June 2012.
Dugdale, D. (2010 September 15). Thoracentesis. MedlinePlus Medical Encyclopedia. [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003420.htm. Accessed June 2012.
Sources Used in Previous Reviews
Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 904-909.
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 868-869, 1535-1536.
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition]. pp 1496.
Forbes, B. et. al. (© 2007). Bailey & Scott's Diagnostic Microbiology, Twelfth Edition: Mosby Elsevier Press, St. Louis, Missouri. Pp 904 – 913.
Schriber, A. (2007 November 12). Pleural fluid analysis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003624.htm. Accessed on 6/21/08.
Kaufman, D. (2006 August 7, Updated). Thoracentesis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003420.htm. Accessed on 6/21/08.
Kaufman, D. (2006 August 7, Updated). Pleural effusion. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000086.htm. Accessed on 6/21/08.
Kaufman, D. (2006 May 3, Updated). Pulmonary actinomycosis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000074.htm. Accessed on 6/21/08.
Garlipp, C. et. al. (2008 January 18). Pleural Effusions: Stability of Samples for White Blood Cell and Differential Counts. Medscape from Laboratory Medicine [On-line information]. Available online at http://www.medscape.com/viewarticle/568386 through http://www.medscape.com. Accessed on 6/21/08.
Lababede, O. (2007 August 10). Effusion, Pleural. eMedicine [On-line information]. Available online at http://www.emedicine.com/radio/TOPIC233.HTM through http://www.emedicine.com. Accessed on 6/21/08.
(2007 August). What Are Pleurisy and Other Disorders of the Pleura?. NHLBI [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/pleurisy/pleurisy_whatare.html through http://www.nhlbi.nih.gov. Accessed on 6/28/08.
Knight JA, Kjeldsberg CR: Cerebrospinal, synovial, and serous body fluids. In Henry's Clinical Diagnosis and Laboratory Management by Laboratory Methods, 21sted. MCpHerson RA & Pincus MR, eds. Saunders:New York, pp 426-454, 2006.