What is pleural fluid analysis?

Pleural fluid analysis is the analysis of pleural fluid in the laboratory that occurs after a pleural tap, or thoracentesis.

A thoracentesis is 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, will show up on a chest X-ray, CT scan, or ultrasound.

Your doctor will perform a thoracentesis 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 doctor has drained the excess fluid, they’ll send it to the laboratory to determine the contents of the fluid and likely cause of the fluid buildup.

Why pleural fluid analysis is used

Doctors use 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 remove larger amounts of fluid to ease discomfort, allowing you to breathe more comfortably.

Thoracentesis is done with caution if you’re taking blood thinners, such as warfarin (Coumadin), due to the risk of bleeding. Depending on the medication you’re taking, your doctor will determine when you need to stop taking that medication before the procedure.

Your doctor likely won’t recommend the procedure if you have severe clotting problems or a known history or clear signs of heart failure.

How a thoracentesis is performed

Thoracentesis is performed under local anesthetic by a doctor in a hospital or same-day surgery setting. Before the procedure, you can expect to have a chest X-ray, a CT scan, or an ultrasound of your chest. Blood tests are used to confirm that your blood is clotting normally. Thoracentesis can be done during a hospital stay or as an outpatient procedure, meaning you can go home afterward.

When you arrive for the procedure, you’ll be asked to change into a hospital gown. You’ll sit on the edge of an armless chair or on a bed. A 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 doctor 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. A small area of your back, between your ribs, will become numb.

After the area is numb, your doctor will insert a 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 pleural fluid 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 a compound known as lactate dehydrogenase (LDH). It’s most commonly the result of inflammation caused by an infection of the lungs, such as pneumonia or tuberculosis. An exudate can also be related to cancer.

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

The levels of protein and LDH in pleural fluid are compared to those levels found in your blood to determine what is considered too high or low.

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 bacterial infection.

If the pleural fluid analysis suggests cancer, your doctor will probably recommend further tests including a closer evaluation of the lungs and other organs.

Risks of thoracentesis

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, requiring repeated procedures

A small pneumothorax will heal by itself, but a larger one usually requires hospitalization and placement of a chest tube.

Aftercare for a thoracentesis

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

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