The Plain Facts About Pleural Fluid Analysis

Written by Debra Stang | Published on August 7, 2012
Medically Reviewed by George Krucik, MD

What Is Pleural Fluid Analysis?

Pleural fluid analysis is also known as thoracentesis. It is a procedure used to drain excess fluid from the space outside of the lungs and inside of the chest cavity. Normally, this area contains about 20 ml of clear to yellow-colored fluid (MedlinePlus).

If there is excess fluid in this area, it can cause symptoms such as shortness of breath and coughing. An excess of pleural fluid, known as pleural effusion or pleurisy, will show up on X-ray or ultrasound.

A surgeon performs pleural fluid analysis by inserting a hollow needle or catheter into the space between two ribs in the back of your chest. The procedure takes place under local anesthesia. Once the surgeon has drained the excess fluid, he or she will send it to the laboratory to determine the cause of the fluid build-up.

Why Surgeons Use Pleural Fluid Analysis

Surgeons perform pleural fluid analysis to determine the cause of the fluid build-up around the lungs. When the cause is known, thoracentesis may be used to eliminate discomfort, allowing an affected patient to breathe more easily.

Pleural fluid analysis is not used if you are taking blood-thinning medications or if you have a clotting problem. It is also avoided if you have a known history or clear signs of heart failure.

How Pleural Fluid Analysis Is Performed

Thoracentesis is performed under local anesthetic by a surgeon in a hospital or day-surgery setting. Before the procedure, you can expect to have a chest X-ray, an ultrasound of your chest, and blood tests to confirm that your blood is clotting normally.

When you arrive for the test, you will be asked to remove your clothing and put on a hospital gown. You will then sit on the edge of an armless chair or on a bed. The technician will help you lean forward so that your arms and head rest on a small table in front of you. It is important to remain as still as possible during the procedure. The technician will cleanse the skin of your side and back with an antiseptic, which may feel cold.

The surgeon will check the preparations and administers an injection of a local anesthetic. You can expect this to sting, but only for a short while. Then the area in the back of your ribs will go numb. After numbness occurs, the surgeon will insert a large, hollow needle between your ribs so that the excess fluid can drain into collection bottles. As the fluid drains, you may experience some discomfort or a strong urge to cough.

The fluid is then sent to a laboratory for further analysis.


After the procedure is completed and the needle is withdrawn, the technician will place pressure on the wound to control any bleeding. He or she will then apply bandages or a dressing, which you will wear for the next day or so.

Depending on the surgeon, you may be asked to stay for an hour of observation. When you are released from the facility, you can resume normal activities immediately, unless your surgeon tells you otherwise.

Complications of Pleural Fluid Analysis

Although invasive, thoracentesis is considered a minor procedure and requires no special follow- up care. Complications are rare, but can include:

  • pneumothorax (a partial or complete collapse of your lung)
  • bleeding
  • infection
  • accidental puncture wound to liver or spleen (very rare)
  • excess fluid may build up again, depending on your diagnosis

According to Cleveland Clinic, pneumothorax occurs in about 10 percent of people who undergo pleural fluid analysis (Cleveland Clinic). A small pneumothorax will heal by itself, while a larger one usually requires hospitalization and additional surgery.

Interpreting Findings

The lab classifies your fluid build-up as either exudate or transudate.

Exudate is cloudy and normally contains high levels of protein. It is most commonly the result of an inflammation caused by an infection of the lungs, such as pneumonia or tuberculosis. More rarely, it is a symptom of cancer.

Transudate, on the other hand, is a clear fluid that contains little or no protein. It usually signifies the failure of an organ such as the liver or heart.

Your treatment will depend upon the underlying cause of the pleural effusion. You may, for instance, be put on medication and a diet to improve your heart function. You may receive antibiotics to clear up a stubborn infection.

If the pleural fluid analysis suggests cancer, the surgeon will probably suggest further tests including a lung biopsy.

Was this article helpful? Yes No

Thank you.

Your message has been sent.

We're sorry, an error occurred.

We are unable to collect your feedback at this time. However, your feedback is important to us. Please try again later.

Show Sources

Trending Now

The Best Multiple Sclerosis iPhone and Android Apps of the Year
The Best Multiple Sclerosis iPhone and Android Apps of the Year
These best multiple sclerosis apps provide helpful information and tools to keep track of your symptoms, including medication reminders.
Timeline of an Anaphylactic Reaction
Timeline of an Anaphylactic Reaction
From first exposure to life-threatening complications, learn how quickly an allergy attack can escalate and why it can become life threatening.
Migraine vs. Chronic Migraine: What Are the Differences?
Migraine vs. Chronic Migraine: What Are the Differences?
There is not just one type of migraine. Chronic migraine is one subtype of migraine. Understand what sets these two conditions apart.
Numbness, Muscle Pain and Other RA Symptoms
Numbness, Muscle Pain and Other RA Symptoms
The symptoms of RA are more than just joint pain and stiffness. Common symptoms include loss of feeling, muscle pain, and more. Learn more in this slideshow.
Famous Athletes with Asthma
Famous Athletes with Asthma
Asthma shouldn’t be a barrier to staying active and fit. Learn about famous athletes who didn’t let asthma stop them from achieving their goals.