There are two types of allergy test: Skin Prick Testing and RAST (IgE specific) blood testing.
Skin prick testing (SPT) is the procedure that we use in Allergy Ireland. Other major centres such as Crumlin Children's Hospital Ireland (CHI) use the same procedure which is regarded as the gold standard in allergy testing. Both skin prick testing and RAST blood tests are equally sensitive for detecting allergies but skin prick testing has many advantages over RAST IgE testing. SPT can test for a wider range of substances and the results are available within 15 minutes whereas RAST results take days. Both testing methods have roughly a 5% failure rate (false negatives) so in the case of life threatening allergies both tests are carried out before a food allergen challenge is considered.
Skin Prick Allergy Testing
The size of the wheal and surrounding redness on the skin indicates how strongly you are allergic to a particular allergen.
Skin Prick Testing is the gold standard for identifying allergies. It is a safe, fast and virtually painless procedure which can be carried out from the age of 6 months old. We place small droplets of allergens onto the skin with a little scratch and within 15 minutes we have your test results ready for interpretation by our doctors. The size of the wheal and surrounding redness on the skin indicates how strongly you are allergic to a particular allergen but specialist interpretation is essential for this type of test.
The following allergens can be tested:
- Inhalant allergens: tree pollen mix, silver birch pollen, grass pollen, dust mite, feathers, cat/dog/horse dander and mould (alternata & cladasporium).
- Foods: milk, egg, wheat, soya, potato, orange, strawberry, kiwi, chocolate and tomato.
- Nuts/Seeds (where appropriate): peanuts, almonds, walnuts, hazelnuts, brazil nuts, sesame, pine nut, pistachio nut, pecan nut, cashew nut, sunflower seed.
- Fish/Shellfish (where appropriate): cod, mackerel, salmon, tuna, shrimp, lobster, crab, clam, mussels.
If you or your doctor would like you to be tested for something not on our list please contact us by e-mail. For example, if you bring a small sliver of fresh food, the leaf of a specific tree where sap can be squeezed out etc, then that can be tested directly. This is usually done for specific fish you suspect that you might have reacted to if it is not available in allergy extract form.
PLEASE DO NOT TURN UP WITH A SHOPPING TROLLEY FULL OF THINGS YOU WANT TO BE TESTED FOR (it has happened!).
Interpretation of results
Results are immediately interpreted and explained to you by one of our specialist doctors who will then formulate a management plan.
A positive result is measured in millimetres of central wheal and outer flare (redness of skin). There are positive (histamine) and negative (saline) controls to ensure the accuracy of test result.
With inhalant allergens (such as dust mite, pollens, animal hair) the size of the wheal and flare is important but does not always reflect the symptoms. For example a patient will occasionally show a very large wheal and flare (say to dust mites) but not show many symptoms. Equally a relatively small reaction (say to cat hair) in someone only recently exposed to cats is usually very important as within a year of continuous exposure the allergic reaction will probably have increased significantly (as will the patient’s symptoms).
It’s easy to perform an allergy test, the skill lies in interpreting the result in the context of the patient's symptoms. Sometimes there is no link.
Patch Testing is used exclusively to test for allergic triggers in a condition called Contact Dermatitis.
Contact Dermatitis occurs when the skin reacts to a substance which it has been in direct contact with causing a red, itchy rash. The rash therefore occurs in the same distribution as the area of contact. The hands are most often affected. It is found more commonly in women than men, primarily due to nickel found in some jewellery and to acrylate allergy associated with nail cosmetics. Contact dermatitis is particularly prevalent in metal workers, cleaners, painters, hairdressers and health care workers.
Patch Testing uses three strips of test patches containing 36 different substances. These substances tested for are the common chemicals in our daily environment and workplaces that most frequently cause skin reactions. They include fragrances, cosmetics, hair dye, dental metals, suncream, lanolin and adhesives. The patches are then removed and the skin examined by one of our specialist doctors 2-3 days later to give us our results.