Pleural fluid culture

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.

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.

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.

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 provider about the meaning of your specific test results.

Abnormal results may indicate:

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

Risks of thoracentesis are:

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

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.

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 C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.