How are allergies tested for?
There are three methods of reliable allergy testing available.
Skin Prick Allergy Testing and IgE specific blood testing can be used to detect allergies to a wide range of foods and airborne allergens.
Patch testing is used specifically to identify contact allergic triggers in a skin condition called contact dermatitis.
Skin prick allergy testing holds a number of advantages over IgE specific blood testing. It is therefore the principal method of allergy testing used at Allergy Ireland and in all other major allergy centres in Ireland. Allergy Testing at our medical centre in Slievemore Clinic, Stillorgan, Co Dublin is immediately followed by consultation with one of our doctors who will accurately interpret the results and tailor an effective management plan.
Skin Prick Allergy Testing
What is Skin Prick Allergy Testing?
Skin Prick Allergy Testing is a safe, fast and virtually painless investigation which identifies whether a suspected allergy is present. It is performed in clinic and the results are available within 15 minutes. It is vital that the results are interpreted by a doctor.
In cases where a food challenge is under consideration then occasionally both skin prick allergy testing and IgE specific bloods tests are carried out. This depends on the specific case history.
What conditions is Skin Prick Allergy Testing useful for?
Skin Prick Allergy Testing is used to confirm sensitisation in IgE mediated allergic disease. This is important in:
- Food Allergy and Anaphylaxis
- Allergic Rhinoconjunctivitis (Hay Fever) and Chronic Sinusitis
- Chronic Urticaria (hives)
Is Skin Prick Allergy Testing Accurate?
Yes, Skin Prick Allergy Testing is a very accurate. It is a very sensitive test with a sensitivity of 95% which results in a low rate of false negatives. This means that it is very unlikely for the allergy to be present if the test is negative. Thus, the negative predictive value is very strong.
The specificity of skin prick allergy testing ranges from 50-70% depending on the allergen being tested. This means that false positives are possible and explains why it is vital that the results are interpreted by a doctor in the context of a detailed clinical history and examination.
What does Skin Prick Allergy Testing involve?
Skin Prick Allergy Testing involves placing a small droplet of allergen onto the skin and then introducing a tiny amount of each allergen into the skin. This is painless and does not result in bleeding. If allergic sensitisation is present, then a temporary bump called a wheal will form on the skin and the surrounding skin will flare red. There are positive (histamine) and negative (saline) controls to ensure the accuracy of test result.
Which allergens can Skin Prick Allergy Testing test for?
Skin Prick Allergy Testing can test for a very wide range of airborne allergens and foods.
The following allergens can be tested for at Allergy Ireland:
- Inhalant Allergens: House Dust Mite, Pollen (Grass/Tree/Ragweed), Feathers, Animal Dander (Cat/Dog/Horse) and Mould Spores (Alternata & Cladosporium).
- Common Foods: Egg, Cows Milk, Soya, Wheat, Oat, Potato, Tomato, Strawberry, Kiwi, Orange and Cocoa.
- Nuts/Seeds (where appropriate): Peanut, Almond, Cashew nut, Hazelnut, Brazil nut, Walnut, Pecan, Pine nut, Pistachio, Chestnut, Sesame seed, Sunflower seed.
- Fish/Shellfish (where appropriate): Cod, Salmon, Tuna, Mackerel, Prawn, Lobster, Crab, Oyster, Mussels, Scallops.
- Other: Latex
If you would like to be tested for something not listed above please contact us by e-mail. For example, if you bring a small sliver of fresh food then this can be tested directly. This is usually done for specific fish you suspect you may have reacted to if it is not available in allergy extract form.
Can Skin Prick Allergy Testing be used to test for food intolerances?
No, Skin Prick Allergy Testing can not be used to test for food intolerances. Food intolerances do not involve an immune response so there is no medical test that can be used for detection. We recommend exclusion of the suspected food followed by reintroduction in order to check for food intolerance. This is best done under the guidance of a dietitian.
Skin Prick Allergy Test Result Interpretation
It’s easy to perform an allergy test, the skill lies in interpreting the result in the context of the patient's symptoms and clinical history.
What are the requirements for Skin Prick Allergy Testing?
- Antihistamines must not be taken starting 5 days prior to the testing date. This includes oral antihistamines, topical antihistamine nasal sprays (Ryaltris, Dymista) and antihistamine eye drops (Opatanol).
- Skin Prick Testing should not be carried out within 4 weeks of a systemic allergic reaction or anaphylaxis. This is due to the risk of false negative test results.
- Skin Prick Testing should be avoided during pregnancy due to the remote risk of a reaction triggering early labour.
- Steroid creams should not be applied to the area of skin being used for testing within 24 hours prior to the test.
IgE Specific Blood Tests
This method of allergy testing detects whether specific IgE antibodies are present in the blood against a specific allergen. IgE specific blood tests are generally not quite as sensitive as skin prick allergy tests and therefore carry a slightly higher rate of false negative results. This means that skin prick allergy testing is better suited to testing for the presence of a particular allergy.
What are IgE specific blood tests used for?
IgE specific blood tests can be used to test for both inhalant allergies such as house dust mite and food allergies such as peanut allergy. However, they are better suited for use as a backup test when additional confirmation of an allergy's presence or absence is required. This scenario typically occurs when a previously confirmed food allergy has diminished over time and a food challenge is being considered in hospital. In that case it is necessary to have the reassurance of negative skin prick testing and IgE Specific allergy testing before proceeding with a food challenge.
Skin Allergy Patch Tests
What are Patch Tests used for?
Patch Testing is used to detect allergic triggers in a condition called Contact Dermatitis. It does not test for food or inhalant allergies.
What does Patch Testing test for?
Patch Testing tests for common chemicals in our daily environment and workplaces that cause skin reactions when they come in contact with some peoples skin. They include cosmetics, hair dye, fragrances, sun cream, lanolin, dental metals and adhesives. These reactions only occur in sensitised individuals.