| Definition: |
A common antigen such as mumps, Candida, or trichophytin is injected just under the skin (intradermal) to determine if a patient's immune system is able to react to antigens. This test is usually performed at the same time as another skin test.
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| Alternative Names: |
Anergy screen; Anergy panel
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| How the test is performed: |
The 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 is able to react to antigens, 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: |
Adults:
There is no special preparation. People with dermatitis or other skin irritations may have the test performed at different locations on the body.
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:
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| How the test will feel: |
| 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: |
| This test is helpful in determining if a person's immune system is functioning properly. A skin test might indicate no exposure to a particular antigen (i.e., a false negative) when actually the immune system is unable to react to any antigen. An example of this would be a PPD or Tine test for tuberculosis, which might be falsely negative if a patients immune system is suppressed. |
| Normal Values: |
The injection site will show a greater than 5 mm inflammation zone at the test site of the test antigens -- i.e., at the site of the anergy test(s).
There should be less than a 5 mm inflammation zone of the disease antigen. |
| What abnormal results mean: |
| 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: |
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: |
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
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