Alternative names 
Pleural fluid aspiration; Pleural tap

Thoracentesis is a procedure to remove fluid from the space between the lining of the outside of the lungs (pleura) and the wall of the chest. Normally, very little fluid is present in this space. An accumulation of excess fluid between the layers of the pleura is called a pleural effusion.

How the test is performed

A small area of skin on your chest or back is washed with a sterilizing solution. Some numbing medicine (local anesthetic) is injected in this area. A needle is then placed through the skin of the chest wall into the space around the lungs called the pleural space. Fluid is withdrawn and collected and may be sent to a laboratory for analysis (pleural fluid analysis).

How to prepare for the test

No special preparation is needed before the procedure. A Chest x-ray is may be performed before and after the test.

Do not cough, breathe deeply, or move during the test to avoid injury to the lung.

Infants and children:
The preparation you can provide for this test depends on your child’s age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

How the test will feel

You will on a bed or sit on the edge of a chair or bed with your head and arms resting on a table. The skin around the procedure site is disinfected and the area is draped. A local anesthetic is injected into the skin. The thoracentesis needle is inserted above the rib into the pleural space.

There will be a stinging sensation when the local anesthetic is injected, and you may feel a sensation of pressure when the needle is inserted into the pleural space.

Inform your health care provider if you develop Shortness of breath or Chest pain .

Why the test is performed

The test is performed to determine the cause of the fluid accumulation or to relieve the symptoms associated with the fluid accumulation.

Normal Values

Normally the pleural cavity contains less than 20 milliliters of serous fluid.

What abnormal results mean

The analysis of the fluid will indicate possible causes of pleural effusion such as infection, cancer, heart failure, Cirrhosis, and kidney disease. If infection is suspected, a culture of the fluid is often done to determine whether microorganisms are present and if so, to identify them.

Additional conditions under which the test may be performed include the following:

  • Pneumonia  
  • Hemothorax  
  • Pulmonary veno-occlusive disease  
  • Pancreatitis  
  • Pulmonary embolism  
  • Thyroid disease  
  • Collagen vascular disease  
  • Asbestos-related pleural effusion  
  • Drug reactions

What the risks are

Special considerations

A Chest x-ray is often done after the procedure to detect possible complications.

Johns Hopkins patient information

Last revised: December 4, 2012
by Amalia K. Gagarina, M.S., R.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.