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HealthInfo Canterbury

Allergy testing

Your doctor will get a lot of information about what might be causing your allergy by examining you and finding out when and where you get symptoms. So it's helpful to keep a diary of your symptoms and what triggers them. They may ask for further tests to confirm which substances trigger your symptoms – we call these allergens.

Skin prick testing

Canterbury Health Laboratories runs an allergy skin prick testing clinic. You will need to be referred to this clinic by a doctor. Some physicians may perform skin prick testing privately.

This test looks at how your body responds to specific allergens. A solution containing the allergen is put on your skin and your skin is then pricked. If you are allergic to that particular allergen, you will develop a red bump, or weal, within 20 to 30 minutes.

The test won't work properly if you are taking antihistamines. Stop all antihistamines at least 72 hours before your test. The test is also not reliable if performed within six weeks of anaphylaxis or an acute allergic reaction to food.

If you have no reaction, it means you are not allergic to that substance and it is not causing your symptoms. But if you do get a red bump, or weal, it means your immune system does react to that allergen.The larger the weal, the more likely it is that you are allergic to that substance and it is causing symptoms.

If a reaction occurs when you are tested but you usually have no symptoms when you are exposed to this substance, then you are sensitised to it rather than allergic.

Skin prick testing is useful for:

Skin prick testing is not useful for:

Examples of substances tested:

The test does not cover most drugs and respiratory irritants, such as household cleaners.

RAST/EAST blood test

This is a blood test that looks for antibodies to specific allergens. If it finds them, it means your immune system is reacting to those allergens. It performs a similar role to skin prick testing, so you only need to do one or the other test, not both.

EAST blood tests are useful when you can't do a skin prick test, for example if you have extensive eczema, or can't stop taking antihistamines.

It is important to identify just a few key allergens if you are going to have one of these tests. To help your doctor with this, keep a diary of your symptoms for several weeks.

Patch testing

This is different to skin prick testing and is usually done by a dermatologist. It is used to test for allergens that cause contact dermatitis (a local skin inflammation that happens when you come in contact with something).

You can find out more information on patch testing on DermNet NZ.

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Written by HealthInfo clinical advisers. Updated October 2015.

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