A cytology examination of pleural fluid detects the presence of cancerous (malignant) cells. The pleural space surrounds the lungs and normally contains only enough fluid to lubricate the lining of the lung (pleura).

The test is performed by inserting a needle into the pleural space to draw off a sample of pleural fluid (the procedure is called thoracentesis). The sample of fluid is examined under the microscope for the presence of abnormal cells.

Food or fluid is not restricted. Do not move, cough, or breathe deeply during the test.

The skin is cleansed, and shaved if necessary, around the insertion site. Local anesthetic to numb the site may be injected into the skin. You may feel pressure or a sticking sensation as the needle enters the skin and pleural space. Inform the health care provider if you develop shortness of breath after the test.

The test is performed to determine the cause of fluid accumulation in the pleural space (pleural effusion), or when cancer is suspected.

Normal cells are seen.

In an abnormal test, malignant (cancerous) cells are present and may indicate a cancerous tumor. This test most often detects breast cancer, lung cancer, and lymphoma.

Additional conditions under which the test may be performed include cancer that has spread to the lung.

The risks include:

• Bleeding
• Infection
• Collapse of the lung (pneumothorax)
• Re-accumulation of fluid, and a shifting in the location of chest structures (mediastinal shift), which can put pressure on blood vessels.

Abeloff MD, Armitage JO, Niederhuber JE, Kastan MB, McKenna WG. Clinical Oncology. 4th ed. Philadelphia, Pa:Churchill Livingstone; 2004.

Light RW. The undiagnosed pleural effusion. Clin Chest Med. June 2006;27:309-319.