What to Expect with an Allergy Scratch Test

By staff

You know you have allergies; you’re just not sure to what it they are to. You have decided to seek diagnosis from an allergist. You are ready for your appointment, but just not sure what to expect. What will they do? How soon will you get results? Will they be reliable? Will it hurt?

As with any doctor appointment, there are mixed feelings. There is anticipation and excitement; you are on your way to feeling better. There is worry and fear, what will the results tell me? There is nervousness, will it hurt? Maybe you know what to expect, maybe you don’t. Here is a brief rundown of what to expect from your visit to the allergist and what your skin test results will tell you.

First, a doctor may decide to do one of three tests to diagnose your allergies, a skin or scratch test, an intradermal test or a blood test. Right now, I’d like to focus on the scratch (or skin test). The doctor will use a comb like object and prick your skin (usually on the back or arm) and a small amount of the possible allergen is put into the skin. This is a fairly safe procedure and the results can be read in usually 15 to 20 minutes. It is also done right in the office and usually on the first visit to an allergist.

Usually a drop of the allergen extract is used, but in some cases, small amounts of the actual allergen are used. When my daughter went through allergy testing, they actually put peanut butter on her skin. Up to 40 different allergens can be tested at once. A positive and negative control are also used, usually histamine (which causes a reaction in everyone) and saline (which doesn’t bother anyone). Does the actual pricking part hurt? Most people say no, but, honestly, my daughter thought it was pretty bad.

After the allergen or extract, for instance cat dander, fescue grass or peanut butter, has been on (or in) your skin for a specific length of time, the results are read. If there is no change in your skin, the results are negative and you are not allergic to the allergen. If there is swelling around the prick site, then the result is positive and you are allergic. The terms wheal and flare are used and these look like mosquito bites around the area. The bigger the wheal, the more allergic you are. Some doctors go by numbers, for instance 0-5, with 0 being negative and 5 being severe.

Because this is done in the doctor’s office, it is a safe (though possible uncomfortable procedure). After the test results are read, the allergen is wiped off and if necessary, cortisone or an antihistamine is applied. The wheals will disappear shortly.

How reliable are the results? They can be reliable as long as no antihistamines or antidepressants are being taken at the time of testing. The most reliable allergens for skin testing are pollen, dust mites and pet dander (airborne allergies). Food allergies are not so reliable. You may get different readings at different times or exhibit a positive skin test but never react to it in daily life. Some allergists require further testing or maybe follow up in a year of so.

Allergy tests can be helpful in diagnosing allergies and take a lot of the guesswork out of what it is you are allergic to. Hopefully, this will prepare you for your visit and help you in using your results to come up with your own health plan.

- Heather Legg

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