What is an intradermal skin test?

An intradermal skin test is a medical procedure used to assess a person's immune response to specific allergens or microorganisms. It is performed by injecting a small amount of the allergen or antigen (a substance capable of inducing an immune response) just beneath the skin's surface. The test is used to diagnose certain allergies, infections, or immunodeficiencies.

Here's how an intradermal skin test works:

1. Preparation: The skin is cleaned and disinfected at the site where the test will be performed, usually on the forearm or upper back.

2. Injection: A small amount of the allergen or antigen is injected into the superficial layer of the skin using a thin needle. The injection is made just below the epidermis, into the dermis.

3. Observation: After the injection, the skin reaction is monitored and evaluated over a specific time period, usually 15 to 30 minutes for immediate reactions or 24 to 48 hours for delayed reactions.

4. Interpretation of Results: The test site is observed for signs of a reaction such as redness, swelling, or a raised bump (wheal) at the injection site. The size and appearance of the reaction can help healthcare professionals determine whether the person is allergic to the tested substance or if they have an immune response to the antigen.

5. Positive and Negative Controls: In addition to the allergen or antigen, control injections are also administered. These include a positive control, which is usually a known allergen, and a negative control, which is typically a saline solution. The purpose of these controls is to ensure that the test is working correctly and to rule out any false-positive or false-negative reactions.

Intradermal skin tests are commonly used to diagnose allergies to substances like pollen, dust mites, pet dander, or certain foods. They can also be used for testing for some infectious diseases, such as tuberculosis (TB) or fungal infections. Immunodeficiency testing, such as allergy testing for immunoglobulin E (IgE), can also be performed using intradermal skin tests.

It's important to note that intradermal skin tests must be performed and interpreted by a trained healthcare professional, usually an allergist or immunologist. These tests are crucial for diagnosing allergies and guiding treatment plans accordingly.