Allergy testing

Allergy testing

If you suffer from allergies and you’re not sure what’s to blame, you may be advised to undergo allergy testing by your doctor. An allergy test will help you to find out which specific allergen is causing your symptoms and forms an important part of your treatment plan, which may include lifestyle changes, allergen avoidance and medication.

How is an allergy test performed?

Allergy testing involves exposing the skin to different allergens and checking the area for any sign of an allergic reaction. If an allergen causes a reaction in the skin, you will experience reddening, swelling or an itchy, raised bump where the substance was applied. When this happens, the skin test indicates that the person has an allergy. If there is no reaction, the test is negative which suggests the person does not have that specific allergy. The size of the swelling determines how severe the allergy is: a large area of swelling shows a higher sensitivity to the allergen in question. Allergy skin tests are usually done at a doctor’s office and take between 20 and 40 minutes to complete. Some tests have immediate results, while others show delayed allergic reactions, which may only develop over a few days.

Types of allergy tests

There are three types of allergy skin tests: Skin prick tests, intradermal tests and patch tests.2 Skin prick testing is the most common allergy test, as it’s quick, convenient and less expensive than the other methods of testing. The results are available within 20 minutes, so you can discuss the outcome with your doctor on the same day as the test. The test is usually performed on the forearm, which is cleaned with alcohol. Drops of commercially produced allergens are placed on marked areas and a sterile lancet is used to make a slight prick in the skin. This ensures that a small amount of the substance enters the skin. The area is then observed for redness and swelling for 15 to 20 minutes.4 This test is most often used to detect allergies to mould, pollen, pet dander, dust mites and insect venom.

Intradermal tests are most often performed when insect venom is the suspected allergen. The allergen extract is injected under the skin and the area is then observed for 15 to 20 minutes. Intradermal testing is more accurate and is usually used when the results of a skin prick test are inconclusive.2 Patch testing is used for allergic skin irritation and detects delayed allergic reactions. This form of testing does not require any needles. The allergen is placed on a patch, that is then applied to the skin for up to 48 hours. A patch test allows for up to 30 allergens to be tested at once, including fragrances, latex, hair dyes, metals and preservatives. After the allotted time, the person being tested returns to the doctor and the patches are removed. Skin irritation at the patch site may indicate an allergy.

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Which allergens can be tested for?

Allergy testing is usually performed in cases of suspected hayfever, or reactions to certain foods and  insect venom. When testing for hayfever, the substances used usually include house dust mites, cat and dog dander (other animals may be included where relevant e.g. horses), mould spores, and pollen from weeds, grasses and trees. In some cases, occupational allergens may be included if the person comes into contact with them during their daily work.

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Allergy testing may not be suitable for everyone. People with severe skin conditions may be advised not to take the test, as it is usually carried out on the skin of the arm or back and there may not be enough unaffected skin to obtain accurate results. Also, in cases where people are highly sensitive to suspected allergens, a test may provoke a severe allergic reaction and is not advisable. For this reason, allergy testing should only be carried out in a medical office that has emergency medical equipment. If you experience shortness of breath, an extensive rash, fever, difficulty swallowing or swelling of the mouth within an hour of an allergy skin test, seek urgent medical attention. These symptoms may indicate a severe allergic reaction.

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