Pleural fluid culture is a test that examines a sample of fluid that has collected in the pleural space to see if you have an infection or understand the cause of buildup of fluid in this space. The pleural space is the area 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.
How the Test is Performed
A procedure called thoracentesis is performed to get a sample of pleural fluid. The sample is sent to a laboratory and examined under a microscope for signs of infection. The sample is also placed in a special dish (culture) to support the growth of microorganisms. It is then watched to see if bacteria or any other germs grow. This can take several days.
How to Prepare for the Test
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.
How the Test will Feel
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 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 provider if you have sharp chest pain or shortness of breath.
Why the Test is Performed
Your provider may order this test if you have signs of a certain infection or if a chest x-ray or CT scan of the chest shows you have too much fluid in the space around the lungs.
A normal result means no bacteria or fungi were seen in the test sample.
A normal value is no growth of any bacteria. Talk to your doctor about the meaning of your specific test results.
Culture - pleural fluid
Blok BK. Thoracentesis. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges' Clinical Procedures in Emergency Medicine and Acute Care. 7th ed. Philadelphia, PA: Elsevier; 2019:chap 9.
Parta M. Pleural effusion and empyema. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 68.
Review Date 11/23/2021
Updated by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.