Researchers warn food allergy blood tests should never be used as standalone diagnostics

Published on December 26, 2011 at 8:28 AM · 1 Comment

New report includes guidelines on whom and when to test

An advisory from two leading allergists, Robert Wood of the Johns Hopkins Children's Center and Scott Sicherer of Mt. Sinai Hospital in New York, urges clinicians to use caution when ordering allergy tests and to avoid making a diagnosis based solely on test results.

In an article, published in the January issue of Pediatrics, the researchers warn that blood tests, an increasingly popular diagnostic tool in recent years, and skin-prick testing, an older weapon in the allergist's arsenal, should never be used as standalone diagnostic strategies. These tests, Sicherer and Wood say, should be used only to confirm suspicion and never to look for allergies in an asymptomatic patient.

Test results, they add, should be interpreted in the context of a patient's symptoms and medical history. If a food allergy is suspected, Sicherer and Wood advise, the patient should undergo a food challenge - the gold standard for diagnosis - which involves consuming small doses of the suspected allergen under medical supervision.

Unlike food challenges, which directly measure an actual allergic reaction, skin tests and blood tests are proxies that detect the presence of IgE antibodies, 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. 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.

These tests can tell whether someone is sensitive to a particular substance but cannot reliably predict if a patient will have an actual allergic reaction, nor can they foretell how severe the reaction might be, the scientists say. Many people who have positive skin tests or measurably elevated IgE antibodies do not have allergies, they caution. For example, past research has found that up to 8 percent of children have a positive skin or blood test for peanut allergies, but only 1 percent of them have clinical symptoms.

"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 says. "Many children with positive tests results do not have allergic symptoms and some children with negative test results have allergies."

Undiagnosed allergies can be dangerous, even fatal, but over-reliance on blood and skin tests can lead to a misdiagnosis, ill-advised food restrictions or unnecessary avoidance of environmental exposures, such as pets.

In addition, the researchers caution, physicians should be careful when comparing results from different tests and laboratories because commercial tests vary in sensitivity. Also, laboratories may interpret tests results differently making an apples-to-apples comparison challenging, Wood says.

In their report, the scientists 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).

Conversely, skin and blood tests should NOT be used:

  • As general screens to look for allergies in symptom-free children.
  • In children with 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.
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  1. Melinda ln48 Melinda ln48 United States says:

    These are horrible, illogical, unscientific conclusions:

    ..."never to look for allergies in an asymptomatic patient"
    ..."research found that 8 percent of children have a positive blood test for peanut allergies, but only 1 percent have clinical symptoms."

    What are these clinical symptoms? Basically they're looking for hives (or anaphylaxis).

    However, there are 1,000 other symptoms that are commonly overlooked: Mood changes, metabolism changes, blood pressure & heart rate, digestion problems, etc etc...almost none of which can be easily observed in a 10 minute wellness checkup. Lab tests are your friend!

    Another dangerous conclusion...
    ...a "food challenge [is the] the gold standard for diagnosis"

    Again, food challenges are definitely useful, but for example, how would you monitor something like the endocrine system during a 10-minute food challenge in a pediatrician's office?

    Blood tests are simple, inexpensive, & non-invasive (just a few drops of blood on a card, similar to a blood type test). Each test has pros & cons (and flaws), but wouldn't it be prudent for every person (every child and adult) to know this information about themselves?

    Do you suffer from ADHD? depression? mood swings? Well, have you ruled out food allergies? Follow the rule of Occam's razor - some things are quick, easy, & inexpensive to rule out. If your MD doesn't know how to do this, go to a CFMP (it's usually very cheap - my insurance didn't cover it, but I got 2 kids tested for 30 things, for around $100 for both, including office visit).

    In once case, an otherwise healthy adult had bad hypertension for 20 years. Turns out, it was just a food allergy. He had no idea - no hives, no history of anaphylaxis.

    And for Judas sake, if you're going to give your child a vaccine with aluminum, please have them tested for aluminum allergy first. For example, does your little girl get reactions to cheap metal earrings? If so, you've already done a free skin test for metals allergy! If the blood or other test comes back positive, do not inject it in her body! If we could just get our pediatricians to follow basic scientific principles, it would cut down tremendously on vaccine reactions (and cut down on superstitions & fears as well). Quantitative science is the way to go.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News-Medical.Net.
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