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)
- swelling of lips, face, eyes (angioedema)
- swelling of tongue
- tightness in throat
- sneezing and running nose (allergic rhinitis – also known as hay fever)
- teary, red, itchy eyes (allergic conjunctivitis)
- wheeze, cough
- nausea and vomiting
- anaphylaxis – a severe allergic reaction that causes serious breathing problems. Anaphylaxis 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 1–2 hours
- 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 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. This should subside in 1–2 hours.
- 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.
- 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. 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:
- the cytotoxic food test
- the Vega test
- bioelectrical testing
- hair analysis
- pulse test
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 under medical supervision.
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
This page has been produced in consultation with and approved by:
Australasian Society of Clinical Immunology and Allergy (ASCIA)
Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.