Norm of Skin Test for Hypersensitivity
There is no agreement on a threshold value for a positive skin test result.
Usage of Skin Test for Hypersensitivity
Allergies and cat-scratch disease.
Description of Skin Test for Hypersensitivity
An intradermal test using allergen extracts to determine sensitivity to various drugs, materials, and pollens that a client may react to in an allergic manner, such reaction possibly resulting in anaphylaxis. The result is based on an immediate hypersensitivity reaction.
Professional Considerations of Skin Test for Hypersensitivity
Consent form NOT required.
- Obtain an alcohol wipe, 0.1 mL of the test substance in question, and an intradermal 26- or 27-gauge needle.
- Have emergency equipment and medications on hand for possible anaphylaxis.
- See Client and Family Teaching.
- Wipe the skin with an alcohol wipe and let it air-dry.
- Intradermally inject 0.1 mL of the test substance in question in the underpart of the forearm.
- Observe for redness and swelling (a wheal) at the site of the injection.
- Results are read 15 minutes after injection. Assess the wheal size of the skin reaction by measuring the mean wheal diameter (MWD) or the mean of the largest wheal diameter and that perpendicular to it. MWDs of skin tests may be expressed in absolute values (millimeters), or they may be related to the size of a control. An MWD >7 mm has a higher diagnostic value for symptomatic allergies. An MWD greater than or equal to a histamine control also has a greater diagnostic value.
- Assess for anaphylaxis symptoms for ½ hour.
Client and Family Teaching
- Withhold allergy medications and antihistamines for 48 hours before the test.
- Report drowsiness, skin rash or itching, difficulty breathing, and palpitations immediately.
Factors That Affect Results
- A subcutaneous rather than an intradermal injection will produce a false-negative result.
- Most skin tests are available in prepackaged sterile kits.