Know before you go: Allergy tests

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If you have allergies, you’re not alone. More than 50 million Americans have allergies, making them the sixth most common cause of chronic illness. But it’s not enough to know that you’re one of millions who suffer. To treat allergies more effectively, you first need to know what is causing your allergic reactions. Allergy tests are quick and painless ways to find out. Here’s what you need to know about allergy tests before you head to the appointment.
Allergies are the immune system’s response to certain triggers, called allergens. There are a few types of allergies: seasonal allergies like pollen and some types of mold; perennial allergies, which are commonly caused by dust mites, and cat or dog hair; and food allergies. Wheat, eggs, milk, peanuts, tree nuts, soy, fish and shellfish are the most common sources for food allergies, but any food can be an allergen.
If you want to know your specific allergens, you’ll need an allergy test. There are two types: skin tests and blood tests. “Both are equally valid and very good at detecting allergies, and, overall, are considered comparable tests,” says Christopher Webber, MD, an allergist with Sky Ridge Medical Center in Lone Tree, Colorado.
Though both tests are simple and accurate, the blood test is more convenient. According to Dr. Webber, a blood test can be done in your primary doctor’s office at any time of the day, doesn’t require an empty stomach and you don’t need to stop taking allergy medications. The drawback is that the test results take longer to process: you’ll receive them within a week, says Webber.
A skin test must be done at an allergist’s office, according to Weber, and you can’t take antihistamines for five to seven days before the test—but you’ll have results in about 20 minutes. Webber explains the process: an allergist will rub pieces of plastic that have been dipped in various allergens—foods, pet dander, or pollen from different trees, grasses, and weeds—on your back.
A positive skin test will cause a hive or welt that lasts for about 20 minutes. It doesn’t hurt, says Webber. “It is usually very fast, sometimes feels like a small poke that is barely noticeable, does not cause bleeding, and is tolerated at all ages,” he says. “But it does itch. Everyone is worried about the hurt, but forgets the itch.”Webber says that there are two situations that could cause either a false negative or a false positive in an allergy test, and it’s an allergist’s job to interpret the results of the test. About one in four people with seasonal allergy symptoms don’t actually have allergies; instead, they have irritant rhinitis (also called nonallergic rhinitis), which has many of the same symptoms as allergies but the immune system is not involved.

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