MedlinePlus Medical Encyclopedia: Skin test anergy

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Skin test anergy

Contents of this page:
Illustrations Alternative names Definition How the test is performed How to prepare for the test How the test will feel	Why the test is performed Normal Values What abnormal results mean What the risks are Special considerations

Illustrations

CSD skin test

Alternative names Return to top

Anergy screen or panel

Definition Return to top

In a skin test anergy, a common antigen such as mumps, candida, or trichophytin is injected just under the skin. The purpose is to determine if a patient's immune system is reacting properly to antigens in general.

An anergy test is usually just a control for some other skin test that is being performed. Because the anergy test can show whether your immune system is functioning properly or not, it can indicate whether the results of the other skin test are reliable.

How the test is performed Return to top

An antigen is injected just under the skin, usually on the forearm, so that a small lump pushes the skin up. The lump indicates that the antigen has been injected at the correct depth. The site is labeled, usually with an ink pen.

After 48 to 72 hours, if the immune system reacts to the antigen, the skin will appear red or irritated where the antigen was injected. The size and degree of irritation will determine whether you are responding to the antigen. A second visit after 48 to 72 hours is required to have the results confirmed. You may be given washing instructions so that the test will be accurate.

How to prepare for the test Return to top

There is no special preparation. People with dermatitis or other skin irritations may have the test performed at different locations on the body.

In infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

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 Return to top

When the antigen is injected, there is a slight stinging sensation where the needle is inserted. After the reaction begins, the area may itch or burn. Sometimes a strong reaction can turn into a large, red, irritated area.

Why the test is performed Return to top

This test serves as a control for some other skin test, such as a tuberculosis test, to make sure the other test is not giving a "false-negative" result.

For example, a patient might have a negative tuberculosis test. If he or she has a healthy immune system, a negative result generally means that person does not have tuberculosis. But if that person's immune system is suppressed, the negative test result may not be meaningful one way or the other -- because the patient's immune system is not reacting properly to any antigen at all. The idea of an anergy test is to help identify a false-negative result.

Normal Values Return to top

If your immune system is functioning properly, the injection site of the anergy test will show a greater than 5 mm inflammation zone.

What abnormal results mean Return to top

An inflammation zone of less than 5 mm indicates the immune system may be unable to react to any antigen. Other tests, such as serologies, may be performed to determine if the person has been exposed to an antigen, to confirm these results.

What the risks are Return to top

A very small amount of the antigen is injected, so the risks are minimal. Typical reactions include itching and hives.

A patient who is hypersensitive to the antigen may experience respiratory distress or other signs of anaphylactic shock.

Special considerations Return to top

Some skin tests are less accurate than others. A significant number of patients with active tuberculosis have negative tuberculin skin tests (called PPD or Tine tests). Tetanus immunization (vaccine) can cause false positive results for diphtheria (Schick test). Tests for food allergies may be less accurate than disease antigen testing.

Other factors that can affect the test results include:

Where on the body the test is performed (the arm reacts differently than the back)
The time of day (morning tests react differently than afternoon tests)
Proximity (closeness) to other tests
Antihistamines can cause a false negative test (negative results when the antigen should show reaction)
Old antigens are used

Update Date: 1/26/2004

Updated by: Daniel Levy, M.D., Ph.D., Infectious Diseases, Greater Baltimore Medical Center, Baltimore, MD. Review provided by VeriMed Healthcare Network.

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