The pleural fluid Gram stain is a test to diagnose bacterial infections in the lungs.
Gram stain of pleural fluid
How the test is performed
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.
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.
Normally, no bacteria is seen in the pleural fluid.
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
You may have a bacterial infection of the lining of the lungs (pleura).
Broaddus VC, Light RW. Pleural effusion. In: Mason RJ, Broaddus VC, Martin TR, et al, eds. Murray and Nadel’s Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa: Saunders Elsevier; 2010:chap 73.
McCool FD. Diseases of the diaphragm, chest wall, pleura, and mediastinum. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 99.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.