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Pleural fluid analysis is a test that examines a sample of fluid that has collected in the pleural space. This is the space between the lining of the outside of the lungs (pleura) and the wall of the chest. When fluid collects in the pleural space, the condition is called pleural effusion.
A procedure called thoracentesis is used to get a sample of pleural fluid. The health care provider examines the sample to look for:
No special preparation is needed before the test. A chest x-ray will be performed before and after the test.
Do not cough, breathe deeply, or move during the test to avoid injury to the lung.
Tell your doctor if you take medicines to thin the blood.
For thoracentesis, you sit on the edge of a chair or bed with your head and arms resting on a table. The health care provider cleans the skin around the insertion site. Numbing medicine (anesthetic) is injected into the skin.
A needle is placed through the skin and muscles of the chest wall into the space around the lungs, called the pleural space. As fluid drains into a collection bottle, you may cough a bit. This is because your lung re-expands to fill the space where fluid had been. This sensation lasts for a few hours after the test.
During the test, tell your health care provider if you have sharp chest pain or shortness of breath.
The test is performed to determine the cause of a pleural effusion. It is also done to relieve the shortness of breath that a large pleural effusion can cause.
Normally the pleural cavity contains less than 20 milliliters (4 teaspoons) of clear, yellowish (serous) fluid.
Abnormal results may indicate possible causes of pleural effusion, such as:
If the health care provider suspects an infection, a culture of the fluid is done to check for bacteria.
The test may also be performed for hemothorax. This is a collection of blood in the pleura.
Risks of thoracentesis are:
Serious complications are uncommon.
Broaddus VC, Light RW. Pleural effusion. In: Mason RJ, Murray JF, Broaddus VC, et al., eds. Murray and Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa: Elsevier Saunders; 2010:chap 73.
Karcher DS. McPherson RA. Cerebrospinal, synovial, serous body fluids, and alternative specimens. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 29.