A gram stain of a skin lesion is a laboratory test that uses special stains to detect and identify bacteria in a sample from a skin sore. The gram stain method is one of the most commonly used techniques for the rapid diagnosis of bacterial infections.
Your health care provider will remove a sample of tissue from the skin sore. For information on how this is done, see the article on skin lesion biopsy.
The sample is sent to a laboratory, where it is applied in a very thin layer to a glass slide. A series of different colored stains is applied to the sample. A laboratory team member examines the stained slide under a microscope, checking for bacteria. The color, size, and shape of the cells help identify the infecting organism.
No preparation is needed for the laboratory test.
The laboratory test is painless. For information on what it feels like to have the skin sample removed, see skin lesion biopsy.
Your doctor may order this test if you have signs of an infected skin sore. The test is done to determine which bacteria is causing the infection.
The test is normal if no bacteria are identified.
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.
An abnormal result means bacteria have been found in the skin lesion. Further tests are needed to confirm the results.
There are no risks related to the laboratory test. For information on risks related to the removal of a skin sample, see skin lesion biopsy.
A skin or mucosal culture may be done along with this test. Other studies are often done on a skin sample to determine if cancer is present.
Viral skin lesions, like herpes simplex, are examined by other tests or a viral culture.
Skin lesion gram stain
Hall GS, Woods GL. Medical bacteriology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 57.
Updated by: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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