Testing Procedures For Allergies

There are a few tests available to indicate weather a child has specific allergies. These tests are able to determine what substance(s) are causing an allergy.

These tests can include:

•    Skin prick tests 

Selected allergens are applied to the forearm or the back with a dropper, and the skin

gently pricked with a needle. A positive result shows as a red weal or flare on the skin

within 20 minutes.

•    Allergen-specific IgE blood tests (RAST) 

These tests are useful when skin testing is not possible or is inconclusive. A blood sample

is taken and the level of an immunoglobulin associated with allergic reaction (allergen

specific IgE) is measured in a laboratory.

•    Elimination diets and challenge testing 

An elimination diet is used to isolate foods that may be causing an allergic reaction. This

usually takes a number of weeks and involves avoiding foods identified as common causes

of food allergy. No foods or fluids may be consumed other than those specified. If

symptoms improve, foods are added one at a time until symptoms recur (this is known as

‘challenge testing’). Usually, a diary is kept to record any symptoms so they can be linked

to the correct food. This procedure must only be performed under medical supervision.

•    Patch tests 

Are most commonly used to investigate contact dermatitis. Common triggers include

fragrances (for example, in soaps). Patches are applied to the back in adhesive strips. The

area is examined after two and four days. A positive result shows as redness or blisters at

the site of a particular substance.

After an allergy test

After the test, you can expect:

•    If you have a skin prick test, your doctor will examine you for signs of an allergic reaction

    after 20 minutes.

•    Patch tests require further visits at two and four days after they are applied.

•    The results of blood tests may take up to a week to be known.

•    An elimination and challenge diet may take many weeks to provide results.

False reactions can occur with any test, so results need to be assessed with your clinical symptoms. Once the offending allergen or allergens are identified, you should try to avoid or reduce exposure to them in future.

Possible complications

Some people with allergies experience severe reactions when exposed to particular allergens. For example, the red weals associated with skin prick tests can be painful, inflamed and irritated.

Some reactions, such as anaphylaxis, is potentially life threatening. It is important that allergy tests are performed by a qualified health professional that can anticipate and treat any allergic reactions you may have.