What Is Thoracentesis?

What to expect when undergoing this test or treatment

Thoracentesis is a medical procedure to remove some fluid between the lungs and the chest wall. The name derives from the Greek words thorax (“chest”) and centesis (“puncture”). It is used to help diagnose and treat medical conditions causing this fluid buildup, called a “pleural effusion.” Thoracentesis is also known by the term “thoracocentesis.”

Verywell / Catherine Song

Purpose of Thoracentesis

Normally, only a very small amount of fluid should be between the outside of the lung and the chest wall, between the two membranes (pleura) that cover the lungs. But sometimes a medical problem causes more fluid to collect in this area. This is excess fluid is known as a pleural effusion. Over 1.5 million people a year in the U.S. experience such a pleural effusion.

Sometimes, people experiencing a pleural effusion have symptoms like shortness of breath, cough, or chest pain. Other times, a person might not have any symptoms. In this case, pleural effusion might be first observed and diagnosed on another test, like a chest X-ray.

Diagnostic and/or Therapeutic Technique

Thoracentesis removes some of the excess fluid surrounding the lungs when there is a pleural effusion. Sometimes thoracentesis is used as a treatment to decrease symptoms from a pleural effusion. All that extra fluid may make you feel short of breath. Removing some of it may help you feel more comfortable.

Other times, thoracentesis is used in diagnosis. For example, it is likely you will need thoracentesis if you have a new pleural effusion and if the medical reason for it is not clear. Detailed analysis of the fluid in a lab can help identify the source of your problem. This type of thoracentesis usually removes a smaller amount of fluid compared to a therapeutic thoracentesis.

Causes of Pleural Effusion

The most common causes of pleural effusions are the following:

However, other medical causes are also possible, including certain autoimmune diseases and other problems affecting the cardiovascular, gastrointestinal, or pulmonary systems. Certain medications, like amiodarone, may also lead to pleural effusions in some people. Because some of the problems causing pleural effusions are quite serious, it’s important that healthcare professionals perform thoracentesis to help pinpoint the problem.

Sometimes thoracentesis can be used for diagnosis and therapy simultaneously, to provide immediate symptom relief while narrowing in on a diagnosis.

Risks and Contraindications

People with certain medical conditions cannot have thoracentesis safely. For example, thoracentesis is not usually recommended for people with severe respiratory failure or people who don’t have adequate blood pressure. People who are unable to sit still for the procedure are also not able to have it safely. Healthcare providers are also very cautious in giving thoracentesis in people with certain lung diseases such as emphysema or in people receiving ventilator support.

Before the Procedure

Before the thoracentesis, your healthcare provider will talk to you about all your medical conditions, perform a physical exam, and assess your health. This will help ensure that thoracentesis makes sense for you.

You should also review your medications with your clinician. If you take medications that affect your blood (like Coumadin), you might need to not take your medication on the day of the procedure.

Don’t hesitate to ask your clinician any questions you have about the procedure. Are you having the procedure for diagnosis, for therapy, or for both? Will you receive a sedative before the procedure? Will you have ultrasound guidance during your procedure? If not, why not? Will you receive a chest X-ray afterward? Now is your chance to get an idea of what to expect.


The procedure itself usually takes around 15 minutes, though set up and clean up will take longer. You will also need to plan time for monitoring afterward.


Typically, a healthcare provider will perform the thoracentesis, with nurses assisting before and after the procedure. Depending on the situation, it may be performed in a hospital or at a practitioner’s office.

Food and Drink

You’ll typically need to avoid eating and drinking for several hours before the procedure.


If you are having thoracentesis as an outpatient, make sure to bring your insurance card and any necessary paperwork with you. You can plan to wear your usual clothes.

If you will be leaving the hospital after the procedure, you will need to arrange to ride home after the test.

During the Procedure

Your medical team will include your healthcare provider, one or more nurses, and health aids or clinic personnel.


Someone may ask you to sign a consent form. Someone may also mark the appropriate side for the needle insertion.

Before the procedure itself, someone will set-up the tools needed. You’ll also probably be hooked up to equipment to help monitor you during the procedure, like for your blood pressure.

Most commonly, people have thoracentesis when they are fully awake. However, some people opt to take a sedative before the procedure, so they will be awake but sleepy.

Throughout Thoracentesis

During the procedure, most people sit while their heads and arms resting on a table. Less commonly, the medical situation might require the person to be lying down. Someone will surgically drape the area and get it ready for the procedure.

In the past, thoracentesis was often performed at the bedside without any kind of imaging. However, now it is frequently done with the help of ultrasound. This can help reduce the risk of a potential complication, like pneumothorax. So your healthcare provider may use ultrasound to help determine the best place to insert the needle.

Someone will clean the skin around the area where the needle is to be inserted. Then someone will inject the area with numbing medicine, so you won’t feel as much pain when the needle goes in.

The practitioner can then slide the needle between two of your ribs, guiding it into the pleural space. As this happens, you’ll receive instructions to hold your breath. You might have a feeling of discomfort or pressure as this happens. You also might cough or experience chest pain as your healthcare provider draws out the excess fluid around your lungs.

Next the needle will be removed, and the area will be bandaged. In some cases, if it is expected that the fluid will reaccumulate quickly (such as in chest trauma) a drain might be connected before the needle is removed. This allows excess fluid to continue to be removed continuously.

After the Procedure

People need to be monitored after getting thoracentesis, even if they are having the procedure as an outpatient. That’s because thoracentesis sometimes causes complications. If you are doing well, you may be able to go home in an hour or so.

Potential Complications

The most common potentially serious complication of thoracentesis is pneumothorax. Some other possible problems include:

  • Re-expansion pulmonary edema (REPE)
  • Damage to the spleen or liver
  • Infection
  • Air embolism
  • Shortness of breath
  • Pain
  • Bleeding

In some cases, these complications might mean that you will need to stay longer at the hospital. Some might require treatment, such as insertion of a chest tube if you get a large pneumothorax. Other times, monitoring will be enough. The good news is that serious complications are relatively rare, especially when healthcare providers are experienced and use ultrasound guidance to perform the procedure.

Contacting Your Healthcare Provider

If you are having outpatient thoracentesis, contact your healthcare provider promptly if you experience symptoms after going home, like:

  • chest pain
  • bleeding from the needle site
  • sudden difficulty breathing
  • a bloody cough

Medical Imaging After Thoracentesis

Most people don’t need to get medical imaging done after thoracentesis. However, you might need to get medical imaging afterward if your symptoms suggest that you might have a complication from thoracentesis, such as shortness of breath or chest pain from a pneumothorax. This might mean getting an ultrasound at the bedside, or it might mean getting an X-ray. Some institutions also get chest X-rays of their patients even if they aren’t having any symptoms, just to be sure everything went well.

You also might need imaging under other circumstances that increase your risk of complications, such as having multiple needle insertions, having advanced lung disease, if you are on mechanical ventilation, or if a large volume of fluid was removed. Sometimes people also receiving medical imaging after thoracentesis to assess any remaining fluid.

Interpreting Results

If you are having a diagnostic thoracentesis, your fluid will be sent to the lab for analysis. The tests done here may take a day or more to come back. Your clinician can let you know about the specific results in your situation. These results may help your healthcare provider diagnose your specific medical condition.

Tests of Fluid Gathered From Thoracentesis

Fluid from different causes has some different characteristics. The fluid appearance provides some key clues about the general cause of fluid accumulation. Some common tests that might be run on the fluid include the following:

  • Glucose
  • Ph
  • Cell count
  • Protein
  • Tests for bacteria
  • Lactate dehydrogenase

Other tests may be necessary under specific circumstances, like tests for tumor markers or tests for markers of congestive heart failure.

After analysis, you might hear your clinician refer to the pleural fluid as a “transudate” or as an “exudate.” Exudates are thicker fluids that occur when some sort of inflammatory fluid is leaking out from cells. Transudates are thinner and more clear, occurring from fluid flowing out of the lung capillaries. Common causes of transudates are liver cirrhosis or heart failure. In contrast, infection or cancer would be more likely to cause exudates. These terms are just general categories that can help your clinician discover what is going on with your health.

Follow-up: Diagnostic Thoracentesis

Sometimes a diagnostic thoracentesis is inconclusive. That just means that your healthcare provider needs more information to determine the cause of your medical problems. Depending on the context, you might need one or more of the following:

  • Additional blood tests
  • Bronchoscopy (a procedure in which a tube is passed into your bronchial tubes)
  • Percutaneous pleural biopsy (a procedure in which part of the pleural tissue is removed)
  • Thoracoscopy (a procedure in which healthcare providers examine the lung surface)

You also might need a pulmonologist to get involved with your diagnosis and care. If you’ve been newly diagnosed with a medical condition, your medical team will help plan the best treatment for you.

Follow-up: Therapeutic Thoracentesis

The majority of people having therapeutic thoracentesis experience improved symptoms over the next month. However, some people need to have thoracentesis repeated if a pleural effusion comes back due to their underlying medical condition. In this case, your healthcare team will work hard to manage your overall clinical picture.

A Word From Verywell

Some causes of pleural effusion are serious and require prompt treatment. It’s easy to get worried even before you even have results. However, it’s best not to get ahead of yourself. With modern techniques, thoracentesis only rarely causes significant side effects. It is a very helpful diagnostic procedure to help give you the answers you are looking for. Don’t hesitate to ask if you have any questions about how the procedure works or how to best interpret the results from your procedure. 

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  5. Kalifatidis A, Lazaridis G, Baka S, et al. Thoracocentesis: From bench to bedJ Thorac Dis. 2015;7(Suppl 1):S1–S4. doi:10.3978/j.issn.2072-1439.2014.12.45

  6. Schildhouse R, Lai A, Barsuk JH, et al. Safe and effective bedside thoracentesis: a review of the evidence for practicing clinicians. J Hosp Med. 2017 Apr;12(4):266-276. doi:10.12788/jhm.2716

  7. Ault MJ, Rosen BT, Scher J, et al. Thoracentesis outcomes: a 12-year experience. Thorax. 2015 Feb;70(2):127-32. doi:10.1136/thoraxjnl-2014-206114

  8. Mirrakhimov AE, Barbaryan A, Ayach T, et al. Is chest radiography routinely needed after thoracentesis? Cleve Clin J Med. 2019 Jun;86(6):371-373. doi:10.3949/ccjm.86a.17058

Additional Reading
  • National Heart, Lung, and Blood Institute. Thoracentesis

  • Sockrider AM, Lareau S, Manthous C. American Thoracic Society. Thoracentesis.

By Ruth Jessen Hickman, MD
Ruth Jessen Hickman, MD, is a freelance medical and health writer and published book author.