Gram stain of tissue biopsy


This test involves a gram stain (using crystal violet) of a sample of tissue taken from a biopsy.

The gram stain method can be applied to almost any clinical specimen and is an excellent technique for making a general, basic identification of the type of bacteria present in the sample.

How the test is performed
A sample called a smear from a tissue specimen is usually applied in a very thin layer to a microscope slide. The specimen is stained with crystal violet stain and undergoes additional processing before it is examined under the microscope for the presence of microorganisms. Different characteristics such as color, shape and pattern of staining help determine the type of microorganism.

How to prepare for the test
If the biopsy is included as part of a surgical procedure, food and fluid may need to be withheld overnight. If the biopsy is of a superficial tissue, food and fluid may need to be withheld for several hours before the procedure.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:

  • infant test or procedure preparation (birth to 1 year)  
  • toddler test or procedure preparation (1 to 3 years)  
  • preschooler test or procedure preparation (3 to 6 years)  
  • schoolage test or procedure preparation (6 to 12 years)  
  • adolescent test or procedure preparation (12 to 18 years)

How the test will feel
How the test feels depends on the part of the body being biopsied. There are several different methods for obtaining tissue samples. A needle may be inserted through the skin to the specific tissue. An incision through the skin into the tissue may be made with a small excision of the specific tissue. A biopsy may also be taken from inside the body by an instrument that visualizes the inside of the body such as an endoscope or cystoscope. Some form of anesthetic is usually given. Pressure and occasionally mild pain may be felt during a biopsy.

Why the test is performed
The test is performed when an infection of a body tissue is suspected.

Normal Values
The presence or type of organisms depends on the particular tissue being biopsied. Some tissues in the body are sterile (e.g., brain) whereas other tissues normally contain organisms (e.g., gut).

What abnormal results mean
Abnormal results usually indicate an infection in the tissue site. Further tests are frequently needed to identify the specific type of organism involved.

What the risks are
Risks are only associated with obtaining a tissue biopsy and may include bleeding or infection.

Johns Hopkins patient information

Last revised: December 5, 2012
by Potos A. Aagen, M.D.

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