At Ready. Set. Food!, we are committed to empowering parents with the knowledge and tools to make informed decisions about your family's health. In this article, we will make the process of food allergy testing easier for you to understand.
- Diagnosing a food allergy starts at home. Eating an allergenic food is the first and most important allergy test.
- There is no single test that a physician can perform that can diagnose a food allergy. Diagnosing a food allergy involves several steps and can be risky.
- The only time food allergy testing should be pursued is if your child already has a history of symptoms associated with introducing allergens at home.
- "Food sensitivity tests" or "food intolerance tests" are not scientifically proven and many medical organizations have cautioned against their use.
Much confusion surrounds food allergy testing. You may think that one test can determine whether your child has a food allergy. However, it’s not that simple. The truth is, there is no single test that can diagnose a food allergy. Diagnosing and confirming whether your child has food allergies involves several steps.
In this article, we will make the process of food allergy testing easier for you to understand, including important information about when food allergy testing is recommended and the risks associated with "food intolerance testing."
Introducing Allergens At Home: First Step Toward A Diagnosis
Diagnosing a food allergy starts at home. Eating an allergenic food is the first and most important allergy test. You first need to take note of foods that triggered a reaction in your child, including the types of symptoms your child has experienced and when they occurred. In babies, the most common symptoms of food allergy are hives and vomiting. You also need to take note of treatments you gave to your child to ease symptoms.
If your child can eat a certain food safely (without any reaction), they do not have a food allergy. However, a food allergy test would help confirm any food allergies if your child’s history reveals symptoms that are consistent with IgE-mediated food allergies, where the immune system makes antibodies called Immunoglobulin E (IgE) in reaction to a specific food.
IgE-mediated vs. Non-IgE mediated Allergy
IgE-mediated food allergies cause your child’s immune system to react when exposed to an allergenic food. Immunoglobulin E (IgE) antibodies are the cause of this reaction and the reaction usually occurs immediately after the ingestion of the allergen.
With a non-IgE-mediated allergy, the reaction is caused by other parts of the immune system. The reaction is also often delayed and can take up to 2 days to develop. An example of a non-IgE-mediated allergy is a delayed allergy to milk, which can cause blood and mucus in the stool within hours or days of ingesting milk. This type of allergy also often causes gastrointestinal symptoms. Both IgE-mediated and non-IgE-mediated allergies involve the immune system. It is possible for a child to have both types of food allergy.
Food Allergy Testing: What Parents Need To Know
Allergy testing is not always the best option because it has a very high rate of false positives. Over 50% of people with an allergy positive test can safely eat the suspected food, and if that leads a parent to avoid giving allergens, then that can lead to a true food allergy. There is no test that is 100% accurate other than simply introducing allergens to your baby. The only time allergy tests should be pursued is if your child already has a history of symptoms associated with eating a food.
Tests for IgE-mediated Food Allergy
If your child already has a history of food allergic symptoms, here are the 3 tests that will help confirm or diagnose your child’s suspected IgE-mediated food allergy:
Skin Prick Testing
In this test, a tiny amount of allergen will be introduced into the skin’s top layer. An itchy bump or a raised red area will develop within 15 minutes if the body produces an IgE antibody in response to the allergen. The test can possibly produce false positive test results, but a negative result is rarely wrong. In other words, if a skin prick test says that your child does not have a food allergy, it is almost always correct, but if the test is positive for an allergy, it is only correct about 50% of the time. This is why it is recommended for confirming observed food allergies in line with your child’s medical history, but not for screening.
Specific IgE Blood Testing
This blood test measures the levels of IgE that are present in the blood. Like the skin prick test, it has a high negative predictive value, which means a negative result is most likely accurate. But it has a low positive predictive value, which again means there’s a greater chance of getting a false positive result. If high levels of IgE are seen, then food allergy may be diagnosed. This is not a recommended screening test because it can produce falsely elevated results.
Oral Food Challenge
With the oral food challenge, your child will ingest the suspected food allergen under the close supervision of a doctor or an allergist. During the test, the allergist will gradually increase the amount of the suspected allergen that your child will consume. If allergic reactions consistent with IgE-mediated food allergy are observed, then a food allergy may be confirmed.
The test takes anywhere between 4 to 8 hours. “An oral food challenge is the only way to definitively diagnose a food allergy,” writes Board Certified Allergist Katie Marks-Cogan MD in our Parent’s Guide to Food Allergies.
Food Intolerance Testing: Proceed with Caution
Learn more about the difference between a food allergy and food intolerance from our Chief Allergist here.
When testing for allergies, you may also want to know whether the symptoms observed in your child is due to food intolerance. With food intolerances, the reactions are also caused by foods but these do not involve the immune system. You may hear of food sensitivity tests that measure IgG antibody, but these tests are not scientifically proven. Also, many allergy groups have cautioned against using these tests because they can be misleading and risky.
Other unproven tests to watch out for are muscle testing, cytotoxicity testing, electrodermal test, natural elimination of allergy treatment, hair analysis, and pulse testing. These have not been proven effective in determining and diagnosing food allergies.
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