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Pleural Fluid Analysis: The Plain Facts

What Is Pleural Fluid Analysis?

Pleural fluid analysis is also known as thoracentesis. It’s a procedure used to drain excess fluid from the space outside of the lungs but inside the chest cavity. Normally, this area contains about 20 milliliters of clear or yellow fluid.

If there’s 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 chest X-ray or ultrasound.

Your surgeon will perform pleural fluid analysis by inserting a hollow needle or catheter into the space between two ribs in your back. This space between two ribs is called the intercostal space. The procedure typically takes place under local anesthesia. Once your surgeon has drained the excess fluid, they’ll send it to the laboratory to determine the cause of the fluid buildup.

Why Pleural Fluid Analysis Is Used

Surgeons perform pleural fluid analysis to determine the cause of the fluid buildup around your lungs. When the cause is known, thoracentesis may still be used to eliminate discomfort, allowing you to breathe more easily.

Pleural fluid analysis is used with caution if you’re taking blood thinners, such as warfarin (Coumadin). Depending on the medication you’re taking your doctor will determine how long you need to stop taking the medication before the procedure.

The procedure is generally avoided if you have severe clotting problems or if you have a known history or clear signs of heart failure.

How Pleural Fluid Analysis Is Performed

Pleural fluid analysis is performed under local anesthetic by a surgeon in a hospital or same-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’ll be asked to change into a hospital gown. You’ll 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’s 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.

Your surgeon will check the preparations and give you an injection of a local anesthetic. You can expect the injection to sting but only for a short while. The area in the back of your ribs will go numb. After numbness occurs, your 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 procedure typically takes about 15 minutes to complete.

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

Understanding the Results

The lab classifies your fluid buildup as either exudate or transudate.

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

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

Your treatment will depend on the underlying cause of the pleural effusion. Your doctor may give you a 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, your surgeon will probably suggest further tests including a lung biopsy.

Risks of Pleural Fluid Analysis

Although it’s invasive, thoracentesis is considered a minor procedure and requires no special follow-up care. The risks are rare, but they can include:

  • a pneumothorax, which is a partial or complete collapse of your lung
  • bleeding
  • an infection at the puncture site
  • an accidental puncture wound to the liver or spleen (very rare)
  • a buildup of excess fluid again, depending on your diagnosis

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


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

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

Content licensed from:

Written by: Debra Stang
Medically reviewed on: Jan 08, 2016: Steven Kim, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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