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What to Know About Allergy Testing

More than 50 million people in the U.S. are allergic to something, according to the Centers for Disease Control and Prevention, making allergies the sixth leading cause of chronic illness in the country.

An allergy happens when the immune system overreacts to a typically harmless substance, or allergen. As common as they are, allergies can be tricky to figure out, let alone manage, on your own. If you keep waking up to unexplained rashes, suspect the common cold isn’t behind your permanently runny nose or wonder if it’s normal for your mouth to itch that much after you eat fruit salad, allergy testing might be the right move.

Allergists use an arsenal of different tests to make sense of patients’ symptoms and guide treatment decisions. We talked to experts about what different tests entail and what patients should know about getting tested.

Should you get tested for allergies?

Allergy testing isn’t preventive care. Universal allergy screening without symptoms isn’t recommended. “Unnecessary allergy testing can lead to ‘false positive’ results, and may result in lifestyle limitations which do nothing to improve your health,” said Sakina Bajowala, medical director of Kaneland Allergy and Asthma Center in North Aurora, Illinois.

But testing does make sense if you have allergy symptoms, such as sneezing, wheezing, a runny or stuffy nose, itchy or tearing eyes, hives, dermatitis (itchy rash) and brain fog. Allergy tests can identify sensitivity to different types of allergens, including food, medication, cosmetics, chemicals and environmental irritants like pollen, dust, mold, grass, animals and venom.

Allergy testing is performed on both children and adults, but traditionally not on young babies. That said, as of a few years ago, infants four months and older are being tested for peanut allergies if they’ve exhibited skin rashes or have a known egg allergy.

Pregnant women are another population for whom allergy testing isn’t recommended, due to the small risk of having a severe allergic reaction during the testing process. But if a pregnant woman has a concerning allergic reaction, consulting an allergist is still advised.

What happens before testing?

Before a doctor conducts allergy testing, they’ll go over your medical history and allergy symptoms, as well as ask about your lifestyle, e.g., whether you live with pets or work in a dusty office. They will also perform a physical exam and may look at your lungs or sinuses via imaging.

To prepare for an allergy test, you’ll likely need to stop taking any allergy medications, such as antihistamines, for the week before your test. Other medications, including certain antidepressants and herbal supplements, may need to be discontinued as well, according to the Asthma and Allergy Foundation of America. If you’re not sure about whether or not a specific medication will interfere with testing, call your doctor.

Different types of allergy tests

The most common test, and typically the first approach used to understand a patient’s symptoms, is a skin prick test. “We’re able to test for things that are ‘living, including animals, dust mites, pollens and mold spores, as well as foods.”  said Mark Holbreich, an allergist in Indianapolis. “Skin testing does not measure reactions to environmental irritants like cigarette smoke or chemicals.”

The test entails inserting small amounts of allergens under the skin’s surface. “Skin prick testing has been used for over 100 years to test for the prevalence of allergies,” Holbreich said. “In the last 20 years or so, the testing material has been more purified, so it’s more accurate.”

The number of allergens included in a skin prick test depends on a patient’s age and symptoms, said Holbreich. Typically, it’s three to five allergens for babies 4 to 6 months old, up to 18 allergens for preschoolers, and up to 50 for teens and adults.

The test only takes about 15 minutes to administer; allergic reactions, caused by a protein in the blood called IgE, are indicated by wheals, or red itchy bumps.

In an intradermal test, an allergen is injected under the skin with a shot. This test is used when a skin prick test is negative but there’s still a reason to suspect an allergy. This method can test for reactions to environmental allergens and drugs, including penicillin and other antibiotics, but usually not food.

An ingestion challenge tests for food and drug allergies. This test requires a patient to consume increasing amounts of a potential allergen by mouth. Then they’re observed for up to three hours for signs of an allergic reaction. More often than not, ingestion challenges are used “with the intention of proving that a food or drug allergy is not present, rather than to confirm an allergy,” said Bajowala, who wrote the 2018 book The Food Allergy Fix: An Integrative and Evidence-Based Approach to Food Allergen Desensitization.

Blood tests called serum IgE tests can provide more detail about exactly how allergic a patient is to a particular item. “This may offer insight into potential reaction severity,” said Bajowala, “or provide guidance about the likelihood of having tolerance to certain foods, for example, peanuts, baked milk or baked eggs.”

Patch tests are used for allergic contact dermatitis or delayed food allergies, where symptoms don’t show up until at least a day after exposure to an allergen. Common allergens in patch testing include fragrance, ingredients in cosmetics, metals, and preservatives and chemicals.

Patches of allergens are applied to a patient’s back in a grid-like pattern. The patches stay in place for 48 hours, during which time full-body showers and sweat-inducing activities need to be avoided. After two days, the patches are removed. Then, one day later (three days after initial application), the allergist will check for reactivity.

What allergy tests cost

The cost of allergy testing is typically covered by health insurance, and is based on the type of test and number of allergens involved. A skin test, for example, would be much less expensive than a blood test for the same allergen.

If you’re concerned about surprise bills, Bajowala said, “it’s best to ask your insurance carrier if a referral is required to see an allergist, to confirm that the allergy test you need is a covered service and determine what your cost-sharing responsibilities are under the terms of your plan.”

If you test positive, what comes next?

You and your allergist can talk about treatment options, including taking over-the-counter or prescription allergy medication. Allergists may also try immunotherapy, which can be administered as allergy shots, drops or tablets. The goal with this approach, Bajowala said, is to “gradually retrain your immune system to tolerate allergen exposure.”

Some patients won’t need drugs at all; they’ll just need to steer clear of whatever’s causing the allergy. Avoidance is the primary method of managing many food allergies and contact allergies, and your doctor may have resources to make it easier to avoid triggers. For example, patients with fragrance allergies should receive an annually updated list of safe, fragrance-free products.

No matter what treatment approach your doctor recommends, make sure it’s something that works for you and your lifestyle.

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