Pleural Fluid Culture

Written by Christine Case-Lo
Medically Reviewed by George Krucik, MD

What Is a Pleural Fluid Culture?

In order to expand, your lungs have a small amount of “potential” space inside your rib cage. The lungs are also protected by two membranes, called the pleura. One of these membranes covers the lungs (visceral); the other lines the inside of the rib cage (parietal). Both of these layers are important for the proper functioning of your lungs.

Normally, a small amount of fluid lubricates the points of contact between the two pleura layers. A pleural fluid culture is a test to see if this fluid contains any bacteria, viruses, or fungi.

Why Is a Pleural Fluid Culture Performed?

This test is usually performed if a chest X-ray shows that you have too much fluid in the space between the pleura (called a pleural effusion). It is also done if you have signs of certain kinds of infection, such as pneumonia.

There could be a number of reasons why you have a buildup of fluid in the pleural space (also called the pleural cavity), and this test is done to check if an infection is the underlying cause.

How Is a Pleural Fluid Culture Performed?

A sample of the pleural fluid is extracted to test for infection. This sample is obtained through thoracentesis, which is a special procedure to remove fluid from the space between the pleura.

If you haven’t already had a chest X-ray, the doctor will perform one as preparation for the thoracentesis. Then, he or she will insert a numbing agent into a small patch of skin on your back. Once the area is numb, your doctor will insert a needle through the skin until he or she reaches the pleural space.

While the sample is being taken, you will have to lean over while sitting on a chair or bed with your head and arms resting on a table. It is important not to move, cough, or breathe deeply while the sample is being taken. This is to avoid injury to the lung.

Fluid will be drawn out through the needle and stored in a tube. Your doctor may want to take another chest X-ray at the end of the procedure.

The pleural fluid will then be sent to a lab for testing. At the lab, the sample will be put on microscope slides and stained with various dyes. The slides will then be examined under the microscope for bacteria, viruses, or fungi that signal infection.

When the lab testing is complete, your doctor will notify you of the results.

How Do I Prepare for a Pleural Fluid Culture?

No special preparation is necessary. Tell your doctor about any allergies you have to latex or cleaning agents.

What Are the Risks of a Pleural Fluid Culture?

During thoracentesis, there is some risk of bleeding. There is also a risk of fluid buildup in the lung, infection at the puncture site, and pneumothorax (air in the chest). Swelling in the lungs (pulmonary edema) and respiratory distress (breathing difficulties) are also potential risks.

Talk to your doctor about any concerns you have.

What Is a Normal Result for a Pleural Fluid Culture?

A normal result is a sample that contains no bacteria, viruses, or fungi.

What Is an Abnormal Result for a Pleural Fluid Culture?

Abnormal results show the presence of bacteria, viruses, or fungi in the sample of pleural fluid. This may mean that you have an infection in the pleural space, such as pneumonia or tuberculosis.

If left untreated, the infection can lead to serious complications, such as pleurisy, an inflammation of the pleura; empyema, a collection of pus between the pleura; or a lung abscess. You will need medical care and possibly hospitalization to treat pleurisy, which may compromise your ability to breathe.

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