Health Library

Pleural fluid culture

Culture - pleural fluid

Pleural fluid culture is a test that examines a sample of fluid that has been collected in the pleural space to see if you have an infection that may cause a 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 a pleural effusion.

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How the Test is Performed

A procedure called thoracentesis is performed to get a sample of pleural fluid. The sample is sent to a lab 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 thoracentesis procedure.

Do not cough, breathe deeply, or move during the procedure to avoid injuring 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. Your 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.

Normal Results

A normal result means no bacteria or fungi were seen in the test sample. Viruses are not typically detected by a pleural fluid culture.

A normal value is no growth of any bacteria. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

Abnormal results may indicate:

• Empyema (collection of pus in the pleural space)
• Lung abscess (collection of pus in a lung)
• Pneumonia
• Tuberculosis

Risks

Risks of thoracentesis are:

• Collapsed lung (pneumothorax)
• Excessive loss of blood
• Fluid reaccumulation
• Infection
• Pulmonary edema
• Respiratory distress
• Serious complications are uncommon

Related Information

References

Blok BK. Thoracentesis. In: Birnbaumer DM, ed. Roberts and Hedges' Clinical Procedures in Emergency Medicine and Acute Care. 8th ed. Philadelphia, PA: Elsevier; 2026:chap 9.

McCool FD. Diseases of the diaphragm, chest wall, pleura, and mediastinum. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 86.

Parta M, Nussenblatt V. Pleural effusion and empyema. In: Blaser MJ, Cohen JI, Holland SM, et al, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 10th ed. Philadelphia, PA: Elsevier; 2026:chap 70.

Review Date: 12/13/2025  

Reviewed By: Jatin M. Vyas, MD, PhD, Roy and Diana Vagelos Professor in Medicine, Columbia University Vagelos College of Physicians and Surgeons, Division of Infectious Diseases, Department of Medicine, New York, NY. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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