A Gram stain is a test used to identify bacteria. It is one of the most common ways to quickly diagnose bacterial infection in the body.
Urethral discharge - Gram stain; Feces - Gram stain; Stool - Gram stain; Joint fluid - Gram stain; Pericardial fluid - Gram stain; Gram stain of urethral discharge; Gram stain of the cervix; Pleural fluid - Gram stain; Sputum - Gram stain; Skin lesion - Gram stain; Gram stain of skin lesion; Gram stain of tissue biopsy
How the test is performed depends on what tissue or fluid from your body is being tested. The test may be quite simple, or you may need to prepare ahead of time.
The sample is sent to a laboratory.
Your provider will tell you what to do to prepare for the test. For some types of tests, you will not need to do anything.
How the test will feel depends on the method used to take a sample. You may not feel anything, or you may feel pressure and mild pain, such as during a biopsy. You may be given some form of pain medicine so you have little or no pain.
You may have this test to diagnose an infection caused by bacteria. It can also identify the type of bacteria causing the infection.
This test can help find the cause of various health problems, including:
A normal result means that no bacteria or only "friendly" bacteria were found. Some types of bacteria normally live in certain areas of the body, such as the intestines. Bacteria normally don't live in other areas, such as the brain or spinal fluid.
Talk to your provider about the meaning of your specific test results.
Abnormal results may indicate an infection. You will need further tests, such as a culture, to find out more about the infection.
Your risks depend on the method used to remove tissue or fluid from your body. You may have no risk at all. Other risks are rare, but may include:
Plourde AR, Beavis KG. Specimen collection and handling for diagnosis of infectious diseases. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 66.
Wojewoda CM, Stempak LM. Medical bacteriology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 57.
Reviewed By: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.