The pleural fluid Gram stain is a test to diagnose bacterial infections in the lungs.

The test is performed when the health care provider suspects an infection of the pleural space, or when a chest x-ray reveals an abnormal collection of pleural fluid.

Pleural fluid is found in the space around the lungs. In a variety of diseases, an abnormal amount of pleural fluid builds up in the lungs.

A sample of the pleural fluid is needed for this test. For information on how the sample is obtained, see: Thoracentesis

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.

See: Thoracentesis