How to Diagnose Allergies

The diagnosis of allergies is generally made after a series of tests are performed by a physician who specializes in allergies. The type of tests used to diagnose an allergy will depend on the kinds of symptoms present. The two basic types of allergy testing are skin testing and RAST (radioallergosorbent test).

Difficulty: Moderate

Instructions

Learn About Skin Testing

1. Understand the oldest form of allergy testing is skin testing. For more than 100 years, this method of testing for allergic disease has proven successful.

2. Know the process begins with introducing a drop of the allergen on the skin with a needle. The skin is scratched just enough to allow the allergen to penetrate the surface.

3. Allow about 15 minutes after the skin is scratched to obtain results. The allergen is confirmed if it produces a bump that is red and itchy.

4. Understand the safeguards to prove a positive result includes a negative and positive control test alongside the tested allergen. The positive control is usually histamine (which should itch), and the negative (which should not itch) is typically a saline solution. The appropriate reaction to each of these will verify the results of the allergen.

5. Find the intradermal skin test to be used if the prick test results are inconclusive in relation to the patient's history. This process requires injection of the allergen under the top layer of skin.

Learn About RAST

6. Understand that RAST is a blood test that measures the presence of specific allergic antibodies. It is limited in the number of allergens that can be tested.

7. Find RAST effective in the diagnosis of food allergies. The amount of allergic antibody resident in the blood determines the level of allergic response to specific foods.

8. Understand the results from RAST testing take longer than skin pricking. The blood must be processed by appropriate laboratories for final results.

9. Know that people with sensitive skin or those on antihistamine medications cannot have skin testing. RAST is the only option. Other groups of people who must opt for RAST over skin pricking include those taking medication for high blood pressure and those with heart and lung conditions.

Tips & Warnings

• Skin testing is considered less reliable on children under the age of 2 years.
• Use only qualified doctors to perform skin testing to diagnose allergies. While extremely rare, anaphylaxis (whole body allergic reaction) can occur.
• Avoid using the allergen challenge to diagnose allergies. This requires the person to have deliberate exposure to the suspected allergen. This potentially dangerous method should be done only by physicians who are experienced in this type of allergy testing.

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