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Allergies in infants and children are common; in fact, allergy-related disorders are among the leading diagnoses of chronic diseases in children. According to one study, 4 to 6 percent of children have food allergies, 8 to 10 percent have asthma and 15 to 25 percent have allergic rhinitis (hay fever). Collectively, children with allergies miss hundreds of thousands of school days every year.

If your son or daughter has symptoms that may be allergy-related, finding their cause — and a doctor to treat them — can be a stressful experience for both you and your child. But the sooner you can identify the trigger for an allergy, the sooner you can help your child get back to just enjoying being a kid. And while any medical test for a child can be scary, knowing what to expect can lessen appointment-day anxiety.

We’ve put together some information about common methods of testing infants and children for allergies. Use it as a reference to prepare your youngster for a visit to the allergist.

Why does my child need an allergy test?

Infants and children often experience symptoms that raise suspicions of an allergic condition. Allergy testing can help determine whether the symptom of concern is caused by an allergy (for example, is that runny nose the result of an upper respiratory infection or an allergy?) and what the specific allergen might be. Conditions where allergy testing can be particularly useful include:

Cold-like symptoms that last for more than a week and occur around the same time every year may also indicate an allergy. Coughing and wheezing, especially at night, may result from allergic asthma caused by an indoor allergen.

How do allergists test for allergies?

If you suspect that your child has an allergy, see an allergist, who can choose an appropriate method or combination of methods to make a diagnosis. If an allergy is found, your allergist will choose the most suitable therapeutic interventions, which can include avoidance strategies, medication, diet modification and allergy shots.

The diagnostic process usually takes place in the allergist’s office and involves getting a detailed medical history of the child and any family history of allergies or asthma, plus a physical exam and allergy sensitivity testing. Allergists mostly use skin tests, blood tests or elimination tests to detect allergens.

For children who have been diagnosed with asthma, allergy tests can help patients and their families better understand how allergens are affecting their disease and learn how to avoid specific substances, such as dust mites or pet dander, that can worsen symptoms.

Skin Tests

Hypersensitivity skin tests, both immediate and delayed, are useful for detecting allergies to airborne particles, foods, insect stingspenicillin and other substances. The most common, least expensive types of skin tests used for children include:

Percutaneous and intradermal skin tests. These immediate-type skin tests are administered by applying a diluted allergen to a prick or a scratch in the top layer of the skin (percutaneous or scratch test) or by using a very thin needle to inject the diluted allergen into the skin (intradermal test). Both are considered extremely safe and relatively accurate. Percutaneous skin testing is rarely conducted on infants younger than 6 months old; otherwise there is no age limit.

Intradermal testing, which is more sensitive, is used if the allergist strongly suspects a venom or penicillin allergy that was not detected by a percutaneous test. Intradermal tests, though low risk, can cause anaphylaxis in highly sensitive patients. It’s therefore important to be sure that the allergist’s office is prepared to treat life-threatening reactions, which can include a sudden drop in blood pressure, trouble breathing and a rapid increase in heart rate.

The accuracy of these tests can be undermined if children are taking certain medications, such as antihistamines, antidepressants or high-dose long-term steroids. Use of these drugs should be stopped, depending on the medication, three to 14 days before the day of testing. (Asthma medications or short bursts of oral steroids will not affect the results.)

After either type of test is administered, the tested area of the skin is observed for about 15 minutes to see if a reaction develops. A wheal (a raised, red and itchy bump) indicates the presence of the allergy antibody when the child comes in contact with a specific allergen — the larger the wheal, the greater the sensitivity.

Patch tests. These delayed hypersensitivity skin tests can be used to diagnose allergic contact dermatitis that flares when children are exposed to substances like rubber, fragrances or certain metals. Patients are asked to leave the patch test in place for 48 hours and keep it dry. An allergist will check the skin for reactions at specific times after the patch is removed.

Blood (In Vitro) Tests

Allergists can also use a blood test, such as a radioallergosorbent (RAST) test or ImmunoCAP, when skin tests are hard to administer (for instance, if a child is unable to stop taking medication that would obscure the wheal and flare test results). Blood tests may be less sensitive than skin tests in detecting allergies.

Elimination Diet Tests

For a child with suspected food allergies, the allergist may recommend and supervise a weeklong diet that eliminates or isolates foods suspected to cause a reaction. Common culprits are milksoyeggs, peanuts, wheat, tree nuts and shellfish.

The downside to this approach is that an elimination diet may be hard to follow. In addition, it may produce inaccurate or unclear results because of the many food allergens disguised in packaged and processed foods.

Allergists can also administer food challenges, giving patients specific doses of foods in a controlled environment to assess reactions.

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