It Usually Takes A Number Of Weeks, And Involves Allergy Food Testing That Have Been Identified As Common Causes Of Food Allergy

vic.gov., Mar 10, 2005

There is a wide variety of substances that may cause allergic reactions in some people. Allergy testing is the procedure used to determine which particular substances (allergens) are responsible for provoking an allergic reaction. The procedure used depends on the type of allergy but may include skin and blood tests or special diets.
Symptoms associated with allergies
Some of the symptoms associated with allergies include:

Skin rashes - eczema (atopic dermatitis) or hives (urticaria)
Swelling - angioedema
Sneezing and running nose - allergic rhinitis (hay fever)
Teary, red, itchy eyes - allergic conjunctivitis
Asthma
Nausea and vomiting - food allergy
Anaphylaxis - severe allergic reaction, which causes serious breathing problems and can be life threatening.
Medical issues to consider
Before the allergy tests, you need to discuss a range of issues with your doctor, including:
Medical history
Clinical symptoms and when they occur
Possible allergen triggers
Any medicines you take that may interfere with skin prick test reactions, such as antihistamines.
The procedures
Specific tests are required to determine exactly which substance or substances are causing the allergy. These tests include:
Skin prick tests - selected allergens are applied to the forearm or back with a dropper, and the skin gently pricked with a needle. A positive result shows within 20 minutes as a red weal or flare.
Allergen-specific IgE blood tests (RAST) - are useful when skin testing is impossible or skin tests are inconclusive. After a blood sample is taken, the level of allergen-specific IgE (an immunoglobulin associated with allergic reaction) produced 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 for a particular person. It usually takes a number of weeks, and involves avoiding foods that have been identified as common causes of food allergy. No foods or fluids may be consumed other than those specified in the starting diet. If symptoms improve, foods are added one at a time until symptoms occur. 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 (in soaps, for example), nickel (in jewellery, watch buckles and coins) and chrome (in leathers and bricklayers' cement). The reagents are available as patches arranged along adhesive strips. The strips are applied to the back. The area is examined after two and four days. A positive result shows as redness or blisters at the site of a particular reagent.
After the test
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 two and four days after they are applied. The results of blood tests may take up to a week. An elimination and challenge diet may take many weeks to provide results.

Be guided by your health care professional. As false reactions can occur with any test, results need to be assessed in conjunction 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 are potentially life threatening. It is important that allergy tests be performed by a qualified health professional who can anticipate and treat any allergic reactions you may have.

Taking care of yourself at home
Be guided by your health care professional, but general suggestions include:
If you had skin tests, follow all recommendations given by your doctor.
If you are following an elimination diet, be careful not to consume any foods or fluids that aren't allowed. This may affect the results of the test and you may need to start all over again.
Long term outlook
Allergy testing can help a person suffering from allergies find out which particular allergens trigger their symptoms. In some cases, an experienced allergist can offer immunotherapy. This is when the person is exposed to increasing amounts of a particular allergen to the point where they no longer have symptoms when they are exposed to 'normal' amounts of that allergen or, at least, they experience reduced symptoms.

Other forms of treatment
Other forms of treatment for allergies include a combination of:
Avoiding the allergens.
Taking medications to treat the symptoms, including over-the-counter medications available from your chemist (such as corticosteroid nasal sprays or antihistamines).
Using corticosteroids and other medications that may be prescribed by your doctor to help manage your symptoms.
Where to get help
Your doctor
Things to remember
Allergy testing is the procedure used to help find out which particular substances are responsible for provoking an allergic reaction.
The procedure depends on the type of allergy, but can include skin and blood tests or special diets.
It is important that allergy tests are performed by a qualified health professional who can anticipate and treat any allergic reactions and interpret the results.