Allergy Tests

The aim of allergy testing is to establish the correct diagnosis so that the offending allergic trigger can be avoided in future and thus prevent further reactions. Because immediate hypersensitivity reactions are triggered by specific IgE antibody, it is possible to perform allergy testing to detect the presence of this antibody against the substance in question. Allergies can be tested for by skin tests, blood tests or, in certain cases, challenge.

** Allergy Blood tests

Specific IgE tests

This test involves taking a small sample of blood and measuring the amount of specific IgE to the allergen tested is present in the blood. Specific IgE tests are available for a large number of allergens. The test is very convenient, completely safe and can be performed even if the patient is taking antihistamines. Like any laboratory test, specific IgE tests are subject to occasional false positive or false negative results. Because of this, correct interpretation by an experienced physician, taking into account the patient’s clinical history, is essential.

Molecular IgE tests

A new class of specific IgE tests have recently become available which, instead of testing for a mixture of allergic proteins to a particular food or aeroallergen, only test the unique proteins that can cause an allergic reaction. This is also known as component resolved diagnostics. These tests can sometimes help distinguish between more serious allergic reactions and less severe reactions due to cross reactivity with inhaled allergens such as birch pollen (see oral allergy syndrome). Examples of situations where these tests can be useful are peanut, hazelnut, peach, apple, fruit and soy allergies.

Immuno Solid-phase Allergen Chip (ISAC) test

The most advanced diagnostic technology is the ISAC allergy microchip array. Using just a small blood sample, the ISAC array tests for 51 different allergens and 112 different allergen components.

** Skin Tests

Skin-prick tests

This test involves placing a small drop of liquid containing the allergen to be tested on the arm and pricking the top layer of skin with a fine needle. The aim is to introduce a small amount of the allergen into the skin. If specific IgE to the allergen is present, this will cause a small reaction at the site called a wheal and flare reaction. Again, both false positive and negative results can occur and correct interpretation by an experienced physician is essential. Antihistamines affect this test and therefore it is essential to avoid taking antihistamines for at least 5 days prior to the test.

Intradermal tests

This test involves injecting a small amount of liquid containing the allergen to be tested into the dermis (upper layer of the skin) of the arm. This test is very useful for diagnosing immediate and delayed hypersensitivity reactions to drugs.

Patch tests

This test involves adding a small amount of the suspect chemical or substance to special metal discs which are then taped to the skin for up to 48 hours. The results are generally read at 24, 48 and 72 hours. This test is very useful for diagnosing delayed hypersensitivity reactions to chemicals, dyes and metals. Patch tests are usually carried out in a dermatology clinic.

** Challenge Tests

Challenge tests

In certain situations, the only definitive way to make a diagnosis or exclude a diagnosis of allergy is by performing a challenge. In such cases, a small amount of the allergen to be tested, such as a food, is given orally to the patient. Naturally, such a procedure is associated with a risk of a reaction and is only performed in very specific circumstances in a safe clinical environment.