What Is the Main Idea?

This blog post is about the reliable diagnosis of food allergies, which is currently mainly done through the use of oral food challenges. In addition, it refers to the paper “Diagnostic Performance of IgE Anti-Der p 10 to Identify Patients with Shrimp Allergy”, published in the journal International Archives of Allergy and Immunology, which describes one of many studies trying to find new and reliable ways of diagnosing food allergies.

What Else Can You Learn?

The blog post also goes into the differences between food allergies and food intolerances: an important distinction that is often misunderstood.

What Is the Difference between a Food Allergy and a Food Intolerance?

Food allergies are extremely dangerous. If someone has one, it means there is a protein in a foodstuff that causes an anaphylactic reaction from their immune system. This reaction can be life-threatening: Although it may be restricted to skin reactions or a sudden drop in blood pressure, it can also cause the airways to constrict, making it difficult or impossible to breathe. Other effects include nausea and dizziness. Anaphylaxis requires rapid medical intervention.

People with food allergies should carry an EpiPen, which allows them to inject epinephrine into a large muscle, usually the thigh. This medication relaxes the muscles in the airways, stomach, intestines, and bladder; and can increase blood pressure to a safer level. After using an EpiPen, people are still advised to seek medical attention as they may need prescription antihistamines or other support.

Food intolerances are unpleasant, but not necessarily dangerous. If someone has one, it means they have difficulty digesting a certain food, a group of foods, or even a range of different foods. They may suffer bloating, indigestion, cramps, diarrhea, and so on. Skin reactions are also possible. The reaction generally occurs within hours of eating the food.

Medical attention might be necessary as there can be significant impact (e.g., malnutrition due to a lack of proper digestion of food, dehydration from longer-lasting or regular diarrhea, poor quality of life). Note that medical intervention is always advised when a child has a food intolerance, as they can interfere with development.

How Are Food Allergies Diagnosed?

Since the allergic reaction to a food protein can be so serious, it is obviously very important to have a reliable method for diagnosing food allergies. Currently, the commonly used method is an oral food challenge, which works by actually causing an allergic reaction.

Oral food challenges involve giving a patient the food (or the protein from that food) that is suspected to cause an allergy, initially in miniscule quantities that may not cause any reaction. The administrating physician observes the patient for a set period to see if there is any reaction, then gives a slightly larger amount of the food (or protein), and so on. Because the amounts are so small, a severe reaction is not expected. Instead, a mild rash, flushed skin, or hives might develop. If this occurs, the test is concluded and ruled positive (i.e., the patient is allergic to a protein in that foodstuff). Naturally, the patient will then receive something to alleviate the reaction — even a mild allergic reaction can be uncomfortable!

National medical authorities require that oral food challenges only be given by trained medical professionals because there is a small risk of a severe anaphylactic reaction. If this happens, treatment must be administered immediately.

Is This the Only Method for Diagnosing Food Allergies?

Oral food challenges are the only method that is 100% reliable, but there are other methods. Blood tests can also work: A blood sample is taken and tested against various proteins to see if there is a measurable change in the level of the allergy-related antibody immunoglobin E (IgE). However, we do not yet know what the most reliable IgE antibodies are for every food allergy.

A skin prick test can also support diagnosis: Similar to a skin prick test for airborne allergens, a solution containing the protein is placed on the skin, which is then pricked with a needle to allow a small amount under the top layer of the skin. However, a positive reaction from the skin does not always indicate an allergy.

Do Oral Food Challenges Work for Diagnosing Food Intolerances?

The described type of oral food challenge does not work for diagnosing food intolerances because these are digestive reactions, not allergic reactions. Giving someone a miniscule amount of the food will not provoke a digestive reaction; and even giving someone a larger amount will not provoke a quick reaction. Similarly, since a food intolerance is not an allergic reaction, testing for antibody responses or skin responses will not show anything. The best way to diagnose a food intolerance is through elimination diets and food records.

What Is the Paper about?

The paper “Diagnostic Performance of IgE Anti-Der p 10 to Identify Patients with Shrimp Allergy” describes a study done to see if the IgE named anti-Der p 10 would be useful for diagnosing shrimp allergies. This type of study is done to try to find reliable replacements for oral food challenges.

In this case, anti-Der p 10 was found to be a reliable biomarker for predicting a shrimp allergy: Every single patient who was positive for a shrimp allergy in an oral food challenge was also positive for anti-Der p 10.

More studies of this type will be important to identify more IgE antibodies that give similarly reliable results.

A Note about Celiac Disease

Although the symptoms of celiac disease are related to the gut, it is not the same as a gluten intolerance. It is also not a food allergy, although the immune system is involved. Celiac disease is an autoimmune disorder where reactions are triggered by gluten, a protein found in wheat. Therefore, the information in this blog post and in the paper are not relevant for the diagnosis of celiac disease.

In some cases, oral food challenges are given to people who already have a known food allergy. For example, an allergist may order the test to find out if a patient has outgrown the allergy. In clinical trials, oral food challenges help researchers learn how well participants are responding to the treatment under study.

Note: This post is based on an article that is not open-access; i.e., only the abstract is freely available.

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