Pleural fluid is found in the space surrounding the lungs.�To do this test, a sample of� the pleural fluid must first be taken from the patient. This is done using a procedure called thoracentesis, or needle aspiration. An area on the chest is cleansed with antibacterial soap and numbed with local anesthetic. A needle is placed between the ribs, and a sample of fluid is withdrawn from the chest.

The fluid sample is�placed onto a microscope slide and mixed with a violet stain (called a gram stain).�A laboratory�specialist uses a microscope to look for bacteria on�the slide. If bacteria are present, the color, number, and structure of the cells are used�to identify the specific organism.

It is important not to cough, breathe deeply, or move when the fluid sample is being taken. There is no other special preparation for the test.

You may feel a stinging sensation when the anesthetic in injected. You may feel some pressure and slight localized pain when the thoracentesis needle enters the pleural space. A chest x-ray is usually done following the test to be sure the lung tissue was not affected by the test.

The test is performed when infection of the pleural space is suspected or when an abnormal collection of pleural fluid is noticed by chest x-ray.

Normally, no organisms are present in the pleural fluid.

A bacterial infection of the pleura (lining of the lungs) may be present.

There is a risk of internal bleeding into the lung and pneumothorax (collapsed lung). Serious complications are extremely rare.