Slievemore Clinic, Old Dublin Road
Stillorgan, Co. Dublin
Contact details
Contact details
The surface of the skin is rich in MAST CELLS. To cut through a lot of unnecessary medical and scientific jargon, the mast cells hold the body’s memory for allergy, in other words the cells recognise what you are allergic to.
Mast cells are also on the surface of eyes, nose & sinuses, mouth and tongue, throughout your breathing and eating tracts. They also run along the surface of the gut. In allergic reactions the mast cells ‘explode’, releasing a number of chemicals that cause problems. Where the reaction is localised (eg, confined to nose & sinuses & eyes in pollen hay fever) the problems stay localised (itchy eyes, sneezing, blocked nose, sinus congestion). Where the reaction is widespread (eg, exposure to shellfish in a highly allergic patient) the mast cells can ‘explode’ and cause a total body response.
With a skin-prick test the doctor places a concentrated drop of allergy extract onto the skin (usually the forearm but occasionally the back, especially in small children). Each drop contains a test substance such as dust mite, cat hair, horsehair, grass pollen and a specific food. Not every food is available in test form and occasionally fresh food will be used.
The test drop is brought into direct contact with the skin mast cells by pricking the surface and allowing the fluid seep to a lower level. If you are allergic to a specific substance the mast cells underneath will ‘explode’ and a reaction appears. The size of the central blister plus any surrounding skin redness tells the doctor what you are allergic to and how strongly allergic. Small reactions are not as important as large swellings. Large and very irregular reactions suggest high allergy. Large and very irregular reactions to food extracts suggest a possible aggressive allergic response if that food is eaten.
The final explanation will depend on what symptoms you have, what the doctor discovers when he examines and what reactions show on testing.
Almost 1 in very 4 Irish people has some type of allergy. However not all will be sufficiently troubled to require medical intervention. Allergy is on the increase, probably because of environmental and dietary changes.
Finding out what you are allergic to is an important first step to effective allergy treatment. Today allergy tests are more convenient and accurate than ever before. When combined with a detailed medical history, allergy testing can identify the specific things that trigger your allergic reactions.
Adults and children of any age can be tested for allergies.
Allergy testing can be done as skin tests or as blood tests. Usually, allergy tests are done under the guidance of an allergy specialist.
Skin testing is fast and positive reactions usually appear within 20 minutes. Sometimes redness and swelling can occur several hours after skin testing. The delayed reaction usually disappears in 24 to 48 hours, but should be reported to the allergy doctor or nurse.
Skin tests cause little or no pain. However, positive reactions cause annoying itching red bumps which look and feel like mosquito bites. The itching and bumps are gone usually within thirty minutes. We now use Quintest multiple allergen testing which makes the procedure quick, considerably less painful and much more suitable for children.
Before attending for an allergy test you must NOT have taken tablets or liquid of anti-histamine medicines (please note, these are put into many cough bottles). Ideally you should not be using steroid tablets. Anti-histamines block the allergy reaction and could give false results. While steroids are less of a problem we prefer not to test while taking steroids by mouth. Anti-histamine and steroid creams are also potentially troublesome for the same reason. If you have any doubt about medications please check in advance. The following treatments are fine: asthma inhalers and nose sprays (no matter what is in them); eye or eardrops; the drugs Singulair or Accolate; antibiotics; tablets and liquid of drugs called Theophylline. Some simple paediatric preparations such as Dozol and Teedex contain antihistamine and cannot be used before any visit. Also, anti-depressants block allergy tests so I would advise against making an appointment if you are on anti-depressants unless it’s for a fiberoptic naso-endoscopy check only.
An allergy blood test is used when:
Because the blood sample must be sent to a lab for testing, it takes many days to get the results.
Skin tests give fast results. They usually cost less than allergy blood tests. What are the negatives? Young children do not like this type of test. Some medicines can interfere with the tests. In addition, in some people with dark skin it may be hard to read the tests. Also, the skill of the tester may affect the results.
Blood tests are helpful because they involve a single needle prick. Medicine does not interfere with the results. However, it takes a long time to get the results and a blood test (called a RAST test) costs considerably more than a skin prick test. At present a batch of (say) 20 separate allergens tested using the RAST method will cost about €660. However cost is not the main factor in deciding which is the most appropriate for your needs and RAST testing may be advised in certain situations. The test results alone do not diagnose allergies. All test results, from either type of test, must be interpreted together with the medical history.
Any medical test involves some risk. The risk with allergy skin tests is that allergy symptoms might occur during the test. The most common symptoms are itching and swelling of the skin where the tests are. In extremely rare cases a more serious reaction can occur. The risk with allergy blood tests is pain or bleeding at the needle mark and fainting (due to a fear of needles and nothing to do with the test).
Allergy tests help find allergies to pollen, moulds, dust mites, animal dander, insect stings and foods. However we DO NOT test for insect stings and recommend the facility in Blackrock Clinic (Dr Bruce Mitchell) if you wish to have this checked.