Healthy Living

Read This Before You Ask Your Doctor To Test You For Food Allergies

As an allergist, I see many patients concerned that they or their child have a food allergy and often request “testing.” I also receive patient referrals because there tends to be some confusion regarding results.

Unfortunately, diagnosing food allergy is much more complicated than simply ordering a test.

For this discussion, food allergy refers specifically to symptoms caused by an immune response to a food, from an antibody called immunoglobulin E (IgE). A food allergy results in consistent symptoms that occur immediately (within minutes to a few hours) and with every exposure. Symptoms can include:

  • Hives

  • Swelling

  • Difficulty breathing

  • Difficulty swallowing

  • Vomiting

  • Low blood pressure (passing out)

  • Anaphylaxis

  • Death

Food intolerance, on the other hand, is a non-immunologic response that causes mainly gastrointestinal symptoms. These responses are not always consistent, and are not always immediate, and therefore not a food allergy. Symptoms can include:

  • Bloating

  • Gassiness

  • Heartburn

  • Vomiting

  • Constipation

  • Diarrhea

The clinical history is what determines whether a food allergy may be present. If you are eating a food without developing any symptoms, then you are not allergic to that food. You cannot fool the immune system – if you are allergic, you should have symptoms with every ingestion.

So why not test just to be sure? IgE testing is associated with low positive predictive values and high rates of falsely elevated results. Up to 30 percent of the general population will produce IgE towards foods, which is called sensitization. However, only about five percent actually have true food allergy. Thus, based on testing alone, food allergy will be over-diagnosed most of the time.

Food allergy test results should not be referred to as “positive” or “negative.” For skin prick testing, where a small amount of an allergen is introduced to the allergy cells in the skin, the size of the bump/redness indicates the likelihood of an allergy being present. A really big bump would therefore mean a higher likelihood of an allergy. On the flip side, undetectable IgE is pretty reliable in ruling out food allergy.

Blood testing for food IgE is widely available but has the same pitfalls as skin prick testing. With blood tests, the level of IgE is reported on a scale from 0.1 to 100. Unfortunately, many laboratories report any result > 0.1 as “positive” or assign an arbitrary level of severity. Again, the level of IgE only indicates the likelihood of an allergy being present.

The best test and gold standard for diagnosing food allergy is the oral challenge. This is typically performed in a physician’s office after IgE testing. If 1-2 servings of a food are eaten without any problems, then food allergy is not present.

To recap:

· IgE tests alone DO NOT diagnose food allergy.

· IgE tests are not useful screening tests due to high rates of falsely elevated results.

· There are no indications to check a ‘panel’ for food allergies.

· The size of the IgE result merely indicates the likelihood of an allergy being present.

· IgE tests DO NOT indicate the severity of reaction, which is a common misconception. So no, tests cannot show if you are ‘deathly’ allergic to anything.

Often overlooked, IgE tests are only useful in evaluating IgE mediated conditions. Specific foods may cause symptoms, completely unrelated to IgE, i.e. Celiac disease. Thus, as our recent study in Pediatrics described, IgE tests should not be performed. Other types of tests are touted online or by some practitioners. This includes IgG testing, acupuncture, and muscle provocation (hold a food in your hand to see if you get weaker – yes, this is a thing) but these are not validated, nor useful in diagnosing food allergy.

Diagnostic testing for food allergies is complicated and requires careful consideration and understanding of how to interpret results. However, when a patient’s history suggests food allergy, proper testing and interpretation can help arrive at the right diagnosis.

Dr. David Stukus is an Associate Professor of Pediatrics in the Division of Allergy/Immunology at Nationwide Children’s Hospital. In addition to his interest in caring for families with asthma, food allergies and other allergic conditions, he also serves as the Director of the Hospital’s Complex Asthma Clinic. His clinical and research interests focus on asthma and food allergies, especially improving education and adherence for patients and families. As part of his research, Dr. Stukus has created novel technology and educational tools using mobile health apps to improve the care of patients, for which he was recognized with the Nationwide Children’s Hospital Department of Pediatrics Junior Faculty Award for Innovation in November 2013. Dr. Stukus serves as an official spokesperson for the American College of Allergy, Asthma, and Immunology and was elected to the Board of Directors for the Asthma and Allergy Foundation of America in 2014. Dr. Stukus actively participates in social media on twitter through @AllergyKidsDoc. Dr. Stukus obtained his medical degree at the University of Pittsburgh School of Medicine. He completed his residency at Nationwide Children’s Hospital and his fellowship at the Cleveland Clinic. He is Board Certified in Allergy/Immunology and Pediatrics.