Allergy testing

About allergy testing

A wide variety of substances 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 usually includes skin and blood tests or an oral food allergen challenge.

Symptoms associated with allergies

Symptoms associated with allergies can include:

• skin rashes – such as eczema (atopic dermatitis) or hives (urticaria)
• sneezing and running nose (allergic rhinitis – also known as hay fever)
• teary, red, itchy eyes (allergic conjunctivitis)
• wheeze, cough
• nausea and vomiting
• swelling of lips, face, eyes (angioedema)
• swelling of tongue
• tightness in throat
• anaphylaxis – a severe allergic reaction that can be fatal.

Medical issues to consider with allergy testing

Before undergoing allergy testing, you need to discuss a range of issues with your doctor, including:

• your 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.

Testing procedures for allergies

Specific tests are needed to determine which substance or substances 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 sterile lancet. A positive result shows as a red weal or flare on the skin within 20 minutes. This should subside in 1 to two hours. Skin prick tests should only be performed by a healthcare professional who has been trained in the procedure and who knows how to select the allergens, interpret the results and manage any generalised allergic reaction that may occur. Allergic reactions to skin prick testing are rare.
• Allergen-specific IgE blood tests (formerly known as 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 reactions associated with food allergy. This usually takes a number of weeks and involves avoiding foods identified as common causes. 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.
• Oral allergen challenge – this may sometimes be required to confirm diagnosis when the cause of an allergic reaction has not been confirmed. This will normally only be performed (using foods or medications) under the supervision of a clinical immunology/ allergy specialist with appropriate resuscitation facilities immediately available.
• Patch tests – most commonly used to investigate contact dermatitis. Common triggers include fragrances (for example, in soaps), nickel (in jewellery, watch buckles and coins) and chrome (in leathers and bricklayers’ cement). Patches are applied to the back in adhesive strips. The area is examined after 2 and 4 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. This should subside in one to 2 hours.
• Patch tests require further visits at 2 and 4 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.
• An oral allergen challenge may require admission to an outpatient or inpatient clinic at a hospital.

False reactions can occur with any test, so results need to be assessed with your clinical symptoms and medical history. Once the offending allergen or allergens are confirmed, you should try to avoid or reduce exposure to them in future as directed by your clinical immunology/allergy specialist.

Complications from allergy tests

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

Unproven allergy tests

A number of other tests have been misleadingly promoted to diagnose allergies. Such tests include:

• cytotoxic food testing
• Vega tests
• bioelectrical testing
• hair analysis
• pulse tests
• kinesiology.

These tests have not been scientifically validated and the results should not be used for diagnosis or treatment.

Remember, reactions to allergens can be life threatening. Allergy testing should always be conducted by a healthcare professional trained and experienced in the procedure in centres with appropriate facilities to treat systemic allergic reactions (anaphylaxis).

Self-care after allergy testing

Be guided by your healthcare professional, but general suggestions for care after allergy tests 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 are not allowed. This may affect the results of the test and you may need to start all over again.

Where to get help

• In an emergency, always call triple zero (000)
• Your GP (doctor)
• Australasian Society of Clinical Immunology and Allergy (ASCIA)
  • Allergy testing
  • Evidence-based versus non evidence-based allergy tests and treatments
  • Locate a specialist
    
• Allergy and Anaphylaxis Australia