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Regular allergy tests could misdiagnose treatment, result in ill-advised restrictions

Ernie Shannon's picture
Skin allergy test

Two allergists are cautioning clinicians against making an allergy diagnosis based solely on traditional blood and skin-pricking tests.

Johns Hopkins Children’s Center's Robert Wood and Scott Sicherer of Mt. Sinai Hospital in New York City are warning that allergy tests relying only on those two methods could result in misdiagnosis, ill-advised food restrictions, and unnecessary avoidance of environmental exposures. Their comments appear in the January issue of Pediatrics.

Instead, the researchers are urging physicians to weigh heavily the patient’s symptoms and medical history and employ, if a food allergy is suspected, a food challenge. This involves consuming small doses of the suspect allergen under medical supervision. Then, the long-time practice of skin-pricking and the more recent diagnostic tool using blood tests can be used to confirm the suspicion.

According to Wood and Scherer regular allergy tests can expose whether an individual is sensitive to a specific substance, but cannot reliably predict if a patient will have an actual allergic reaction, nor can they foretell how severe the reaction might be.

“Allergy tests can help a clinician in making a diagnosis, but tests by themselves are not diagnostic magic bullets or foolproof predictors of clinical disease,” Wood said. “Many children with positive test results do not have allergic symptoms and some children with negative test results have allergies.”

This is important because at least six percent of all children have one or more food-based allergies, according to the latest estimates from the National Institutes of Health.

Skin and blood tests are proxies, the researchers say, that detect the presence of IgE antibodies that are immune-system chemicals released in response to allergens. Skin testing involves pricking the skin with small amounts of an allergen and observing if and how the skin reacts, Wood says. “A large hive-like wheal at the injection site signals that the patient’s immune system has created antibodies to the allergen. Blood tests, on the other hand, measure the levels of specific IgE antibodies circulating in the blood.”

The scientists also say in the Pediatrics Journal article that many people who have positive skin tests or measurably elevated IgE antibodies do not have allergies. For example, past research has found that up to eight percent of children have a positive skin or blood test for peanut allergies, but only one percent of them have clinical symptoms.

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In their report, Wood and Sicherer say skin and blood tests can and should be used to:

· Confirm a suspected allergic trigger after observing clinical reactions suggestive of an allergy. For example, children with moderate to severe asthma should be tested for allergies to common household or environmental triggers including pollen, molds, pet dander, cockroach, mice or dust mites.

· Monitor the course of established food allergies via periodic testing. Levels of antibodies can help determine whether someone is still allergic and progressively decreasing levels of antibodies can signify allergy resolution or outgrowing the allergy.

· Confirm an allergy to insect venom following a sting that causes anaphylaxis, a life-threatening allergic reaction marked by difficulty breathing, lightheadedness, dizziness, and hives.

· Determine vaccine allergies (skin tests only).

At the same time skin and blood tests should not be used:

· As general screens to look for allergies in symptom-free children.

· In children with a history of allergic reactions to specific foods. In this case, the test will add no diagnostic value, the experts say.

· To test for drug allergies. Generally, blood and skin tests do not detect antibodies to medications.

Image source of Skin Allergy Test: Wikipedia