Allergy testing

A wide variety of substances can cause allergic reactions in some people. Allergy testing is used to find out which particular substances (allergens) are responsible for provoking a 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#

Allergy symptoms can include:

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

Before you are tested#

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

• your medical history
• your 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#

Specific tests are used to find out which substance or substances are causing an allergy.

Skin prick tests#

Selected allergens are applied to the forearm or back with a dropper, and the skin is gently pricked with a sterile lancet. A positive result shows as a red weal or flare on the skin within about 20 minutes, and usually subsides within 1 to 2 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 generalized allergic reaction that may occur. Allergic reactions to skin prick testing are rare.

Allergen-specific IgE blood tests#

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 linked to 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 back one at a time until symptoms return (this is known as challenge testing). A diary is usually kept to record any symptoms so they can be linked to the correct food. This procedure must only be carried out under medical supervision.

Oral allergen challenge#

This may sometimes be needed to confirm a diagnosis when the cause of an allergic reaction has not been established. It is normally performed (using foods or medications) only under the supervision of a clinical immunology or allergy specialist, with resuscitation facilities immediately available.

Patch tests#

Patch testing is most commonly used to investigate contact dermatitis. Common triggers include fragrances (for example, in soaps), nickel (in jewelry, watch buckles and coins) and chrome (in leathers and cement). Patches are applied to the back in adhesive strips and 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#

What to expect depends on the test:

• after a skin prick test, your doctor will check you for signs of an allergic reaction after about 20 minutes, and any reaction should subside within 1 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
• 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 alongside your 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 specialist.

Complications and unproven 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.

A number of other tests have been misleadingly promoted to diagnose allergies, including cytotoxic food testing, Vega tests, bioelectrical testing, hair analysis, pulse tests and kinesiology. These tests have not been scientifically validated, and their 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 who is trained and experienced in the procedure, in a center 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, as this may affect the results and mean you have to start again

Key points#

• A wide variety of substances may cause allergic reactions in some people.
• Allergy symptoms can range from mild to a severe reaction that can be life threatening.
• An elimination diet usually takes a number of weeks and involves avoiding foods identified as common causes.
• If symptoms improve, foods are added back one at a time until symptoms recur (challenge testing).
• A diary is usually kept to record symptoms so they can be linked to the correct food.

Where to get help#