Other blood tests include:

• Absolute eosinophil count
• Total IgE level

PROVOCATION

Provocation (challenge) testing involves exposing a person to a suspected allergen under controlled circumstances. This may be done in the diet or by breathing in the suspected allergen. This type of test may provoke severe allergic reactions. Challenge testing should only be done by a doctor.

Another method is the double-blind test. This method involves giving foods and harmless substances in a disguised form. The person being tested and the provider are both unaware of whether the substance tested in that session is the harmless substance or the suspected food. A third party knows the identity of the substances and identifies them with some sort of code. This test requires several sessions if more than one substance is under investigation.

While the double-blind strategy is useful and practical for mild allergic reactions, it must be done carefully in individuals with suspected severe reactions to foods. Blood tests may be a safer first approach.

Before any allergy testing, the health care provider will ask for a very detailed medical history. This may include questions about such things as illnesses, emotional and social conditions, work, entertainment, lifestyle, foods, and eating habits.

If skin testing will be performed, you should NOT take antihistamines before the test. This may lead to a false-negative result, falsely reassuring you that a substance is unlikely to cause a severe allergic reaction. Your doctor will tell you which medicines to avoid and when to stop taking them before the test.

Skin tests may cause very mild discomfort when the skin is pricked. Itching may occur if you have a positive reaction to the allergen.

Allergy tests are done to determine the specific substances that cause an allergic reaction in a person.

Your doctor may order allergy tests if you have:

• Allergic rhinitis and asthma symptoms that are not easily controlled with medications
• Angioedema and hives
• Food allergies
• Contact dermatitis
• Penicillin allergy*

*NOTE: Allergies to penicillin and closely related medications are the only drug allergies that can be tested using skin tests. Skin tests for allergies to other drugs can be dangerous.

The prick skin test may also be used to diagnose food allergies. Intradermal tests are not used to test for food allergies because of high false positive results and the danger of causing a severe allergic reaction.

Images

Skin testing, PPD (R arm) and Candida (L)

Allergy skin prick or scratch test

Intradermal allergy test reactions

RAST test

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Allergy testing Results

Review Date: 06/25/2011
Reviewed By: David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc., and Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)