First a sample of pleural fluid must be taken from the patient. This is done using a procedure called� thoracentesis, or needle aspiration. A small 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 A needle is placed between the ribs, and a sample of fluid is withdrawn from the chest.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�sample�is placed on culture plates that contain�a substance to help the microorganisms in the fluid grow. When colonies of microorganisms are big enough, a series of tests are�done to identify the infection-causing organisms.

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 shows on a chest x-ray.

Normally, no organisms are present in the pleural fluid.

Abnormal results may indicate pneumonia, tuberculosis, or a lung abscess. Pulmonary nocardiosis is an additional condition under which the test may be performed.

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