A needle is used to aspirate fluid from the pleural space, which lies between the lungs and the chest wall. The fluid sample is sent for laboratory analysis to identify the cause of pleural effusion (excess fluid in the pleural space). Thoracentesis may also be performed therapeutically to relieve symptoms caused by accumulation of pleural fluid.

Purpose of the Thoracentesis

  • To determine the cause of pleural effusion and help select an appropriate treatment
  • To remove a fluid sample from around the lung
  • To relieve symptoms, such as pain and breathing difficulty, which can result from accumulation of pleural fluid
  • To diagnose cancers that spread to the pleura or the lung
  • To evaluate symptoms such as mesothelioma, chest pain and infection (tuberculosis or bacterial) and staging of lung cancer

Who Performs It

  • A physician

Special Concerns

  • Thoracentesis may be performed in a hospital or an outpatient setting.
  • This procedure may not be safe in people with bleeding disorders.
  • A chest x-ray or ultrasound scan may be performed before the test in order to help the doctor locate the pleural fluid and guide needle placement. Alternatively, fluoroscopy, may be done during the procedure.

Before the Thoracentesis

  • Report to your doctor any medications, herbs, or supplements you are taking. You may be advised to discontinue certain drugs before the test. In addition, tell your doctor if you are taking any antimicrobial drugs, such as antibiotics.
  • Tell your physician about any previous bleeding problems you’ve had, what medicines you’re taking and whether you have allergies to latex or medicines.

What You Experience

  • You are asked to remove your shirt and put on a hospital gown. The doctor will advise you to remain still and avoid coughing or breathing deeply during the procedure to reduce the risk of needle damage to the lung or pleura.
  • The doctor will position you in a way that facilitates access to the pleural space—usually sitting upright on a bed or chair with your arms raised and supported on a table, and sometimes lying partially on your side with your arms overhead.
  • The skin at the site of injection is cleansed with an antiseptic, and a local anesthetic is administered to numb the area.
  • The aspiration needle is inserted between two ribs through the chest wall into the pleural space. You will feel pressure during insertion, and may have a very brief sensation of sharp pain as the needle enters the pleural space. In general, only mild discomfort is experienced.
  • Once the needle is inserted, a clamp may be attached to hold it in place. The fluid is withdrawn through the needle into a syringe, and specimen containers are sent immediately to a laboratory for analysis.
  • The needle is withdrawn and a small bandage is applied.
  • The procedure takes 10 to 15 minutes. The procedure may take up to 45 minutes, if there's a lot of fluid.

Risks and Complications

  • Possible serious complications include pneumothorax (leakage of air outside the lungs and into the pleural cavity, resulting in a collapsed lung); bleeding; pain; bruising; spleen or liver injury; infection; inadvertent puncture of the lung or a blood vessel; or, if a large amount of fluid was withdrawn, pulmonary edema (accumulation of fluid in the lungs).
  • The use of ultrasound or fluoroscopy to guide needle insertion may reduce the risk of complications.

After the Thoracentesis

  • Your vital signs will be monitored and you will be observed for any signs of complications for a period of time after the procedure.
  • A chest x-ray will be done to ensure that a pneumothorax has not developed.
  • Inform your doctor immediately if you experience a bleeding from the needle site, pain and difficulty in breathing, and cough that produces blood.


  • The specimen containers may be sent to several different laboratories for examination. The gross appearance of the fluid will be considered, and it will be analyzed for bacteria, white and red blood cells, the presence of unusual cells, and other components.
  • Your doctor may be able to diagnose the cause of the pleural effusion based on results from these laboratory tests, although this is not always possible. Potential causes include pneumonia, tuberculosis, pancreatitis (an inflamed pancreas), cancer, and congestive heart failure.
  • Appropriate treatment will be initiated, depending on the problem.


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 25 Jan 2012

Last Modified: 27 Jan 2015