Food allergy testing 101

Key takeaways:

• Food allergy tests should be ordered by specialists and, if positive, indicate the likelihood of a person reacting upon exposure.
• Broad food allergy panels and other nonvalidated tests are not indicated.

Editor’s Note: In Healio Allergy/Asthma’s column, “Food Allergy: Fact vs. Fiction,” Douglas H. Jones, MD, breaks down what’s true and what’s myth for a variety of topics related to food allergies. If you have a question you would like answered in this column, email Jones at rmaaimd@gmail.com or Sasha Todak at stodak@healio.com.

Every day, patients bring me results of broad panels of tests. Some are validated tests, whereas others are tests that have little to no real clinical data to support their use.

Here is an example scenario that must end:

Patient: “Doctor, I just get stomach aches every time I eat. Is it a food allergy that I don’t know about? Can I get a panel of tests done?”

Doctor: “Well, let’s check it out. I will order a broad panel of food allergy tests to see.”

Many times, the patient and even the doctor who ordered the test do not know how to interpret the results. The tests usually show mildly positive results to many foods that the patient was consuming with no symptoms.

The usual recommendation that I hear is that the doctor will tell the patient to avoid that food for a few weeks and then slowly reintroduce it. The patient will get frustrated as it does not make sense and it is difficult to do, especially because they didn’t have symptoms from those specific foods in the first place. But they still do not feel well when they eat, so what to do?

The first thing is to realize that not every symptom that someone gets from eating is “food allergy.” There are food sensitivities and intolerances, celiac disease, gastroenteropathies, non-IgE-mediated food allergy and many more categories. It is wrong to classify all of those as food allergy. Yet, I hear it all the time, even though doing so is like lumping every person who has seizures or neuropathy as having had a stroke.

Let’s get this cleared up. Here are five important questions to consider:

1. What kind of validated food allergy tests are there?
2. What do food allergy test results really mean?
3. When should food allergy tests be ordered?
4. What tests should be ordered?
5. What about food intolerances and food sensitivity testing?

These are all pertinent questions that many do not understand. Let’s examine them more closely.

What kind of validated food allergy tests are there?

The most common food allergy tests include skin prick testing (intradermal testing should not be done for food allergy as there is a risk of systemic reaction) and serum IgE tests that include the specific foods and component tests to the foods.

There are also investigational tests such as basophil activation tests and epitope testing. These tests are not available everywhere, but they are emerging.

Despite what marketing says, nonvalidated tests that do not correlate with symptoms nor have strong evidence to support their use in food allergy, food intolerance or food sensitivity include:

• IgG testing;
• kinesiology or Nambudripad Allergy Elimination Technique (NAET) testing;
• saliva tests;
• hair analysis;
• electrodermal testing; and
• flow cytometry for WBC morphology.

What do food allergy test results really mean (referencing the common IgE tests through skin tests or serum)?

Does a food allergy test indicate severity of food allergy? Nope.

Do the food allergy severity scales indicate severity? Nope.

Does the higher the number indicate a more severe reaction will occur? Nope.

Does a positive test equal food allergy? Nope.

Does a negative food allergy test rule out food allergy? Nope.

What does it mean, then? A positive food allergy test indicates the likelihood of a person reacting upon exposure. Reread that sentence slowly and digest it, please. Was severity in that sentence? No. Is confirmation of food allergy in that sentence? Again, no.

Food allergy should be determined in the context of a person and their history. Food allergy tests in isolation without a person or history are not helpful. History is most important, and tests are supportive. The numbers associated with each food are not always interpreted the same, either. Food allergy tests must be interpreted in the context of the person and their history and taking into consideration the food in question.

When should food allergy tests be ordered?

Food allergy tests should be considered when there is a history of food allergy symptoms or reaction in a person. Isolated gastrointestinal symptoms are not symptoms of classical IgE-mediated food allergy. Rather, that is more consistent with food sensitivity, food intolerance or perhaps celiac disease. We may also see GI symptoms in non-IgE mediated food allergies such as food protein-induced enterocolitis syndrome (FPIES). These patients are at risk for low blood pressure when their vomiting and diarrhea are severe.

What tests should be ordered?

Specific and targeted food allergy tests based on the patient’s history dictate what should be ordered. Broad food allergy panels to find the “unknown” food allergy are not indicated.

If someone is seemingly reacting to anything and everything or if the reactions are inconsistent and not reproducible, then we start considering other diagnoses besides IgE-mediated food allergy. When in doubt, refer to a specialist so that we are not exposing the patient to unnecessary tests or needle sticks.

There is a widespread problem of food misdiagnosis — usually overdiagnoses, but also occasionally underdiagnosis, even considering the plethora of tests being ordered. Medical school 101 teaches that if we do not know how to interpret a test, then we should not order it. We should refer and defer to those who do know how to interpret the tests and they are the ones who should order them.

I often hear that tests are ordered to try and save me time. However, they usually end up costing me and the patient more time.

What about food intolerances and food sensitivity testing?

There will be a future blog post addressing this issue in more detail. The key takeaway for this article is to please refer to the nonvalidated tests list above and consider the question, “Why are these tests not validated?” Before ordering them, consider researching the data behind them — not from their website, a paid “expert” or from paid advertising, but from actual scholarly articles. I think you will find that they have shown in real clinical trials that the tests results do not correlate with clinical symptoms.

If that is the case, why order them? Are you biting the marketing click bait from those who are in line to profit from the test? Just because a test can be ordered, doesn’t mean it should be ordered.

For more information:

Douglas H. Jones, MD, FAAAAI, FACAAI, is cofounder of Global Food Therapy, Food Allergy Support Team and OITConnect, the director at Rocky Mountain Allergy at Tanner Clinic, and a Healio Allergy/Asthma Peer Perspective Board Member. He can be reached at rmaaimd@gmail.com or on Instagram @drdouglasjones.