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May 13th 2020

A Look at Food Allergy Testing and Diagnoses

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Food allergy prevalence is rising globally. Since there is no effective cure and allergy often comes with life-threatening anaphylaxis, people are advised to steer clear of risky foods and carry an EpiPen. However, a recent study reported in the Journal of the American Medical Association (JAMA) shows that although almost 19% of surveyed adults believe they have a food allergy, only 10.8% fit the criteria based on clinical signs and diagnostic rigor. Food allergy testing with advances in precision medicine could help untangle the myths from the facts, helping a growing population worldwide manage day-to-day life and avoid restrictive dietary practices.

What Defines a Food Allergy?

A food allergy is not a sensitivity or intolerance. It is an immune-mediated response to allergens in foods. When certain foods are eaten, or simply touched or inhaled, these sensitizing markers trigger the immune system into overdrive.

According to the Mayo Clinic, signs of an allergic reaction come on within a few minutes or a couple of hours, and include itchiness and hives, swollen lips, and vomiting among other symptoms. Exposure to an allergen triggers an overwhelming cascade of immune responses, releasing highly potent compounds such as histamine that activate further adverse tissue reactions. Anaphylaxis is the most severe reaction, with constricted airways and a swollen throat. Blood pressure can drop sharply and without treatment, consciousness is lost rapidly leading to coma and death.

While a food intolerance may be uncomfortable, it does not involve an immune response or risk death. As described by the American Academy of Allergy, Asthma and Immunology (AAAI), food intolerance affects the gut; feeling bloated is a commonly reported symptom, along with other gastrointestinal disturbance. Although oral immunotherapy shows some promise as a preventative measure, the only treatment for food allergy is strict avoidance. Intolerance is a lifestyle choice, whereas an allergy isn’t.

Food Allergy Testing

Food allergy testing involves assessing the antibody response to allergen exposure. The Mayo Clinic advises that definitive diagnosis needs a combination of approaches, including skin tests and antibody response.

The Food and Drug Administration (FDA) lists eight common allergens including fish, eggs, shellfish and peanuts. During skin testing, a small amount of the foods is scratched into the skin; allergy shows up as bumps and redness. However, this isn’t definitive, so other tests including dietary challenges are useful. It is worth noting here that measuring antibody levels is only useful if the test is for immunoglobulin E (IgE). Both the AAAI and the Canadian Society of Allergy and Clinical Immunology (CSACI) do not recommend food-specific IgG food allergy testing as it has no scientific basis.

Why the Increase?

A 2017 review in the journal Immunity notes that there has been a sharp increase in people with food allergies over the last two decades but there’s still no conclusive evidence to show why this is happening. Although it’s likely that environmental factors modify risk, the BBC notes that links to increased pollution and antibiotic use have not been proven.

One theory is that increased exposure to novel foods could be driving the increase. As global trade and increased leisure travel bring us into contact with other cultures, our dietary choices also diversify, bringing us novel foods and ingredients to explore. Skin sensitization to peanut oil in diaper cream and wheat proteins in face soap has been linked to food allergy.

Conversely, previous advice on limiting early childhood exposure to allergens may also have caused the increase in food allergy. A review published in Nutrients overturns advice given in the 1990s to avoid peanuts during pregnancy and in infancy. Numerous studies showed that delaying exposure was associated with development of food allergy.

Potential Treatment and Diagnosis

Although there are some potential treatments under investigation, the current cure for food allergy is strict avoidance. There is, however, strong evidence that eating a varied diet from early childhood could help stop many food allergies developing. For example, the LEAP Study in the UK shows that exposing children to peanuts from early infancy reduced incidence of peanut allergy.

Oral immunotherapy, where patients desensitize themselves by eating increasing amounts of the allergen, shows some promise. With successful treatment, patients can eat more of the food before triggering a response. Unfortunately, this only works as a preventive measure and the allergy returns if treatment lapses.

There are also trials looking at epicutaneous immunotherapy, using skin patches to deliver food allergens. However, a recent study in children published by JAMA showed inconclusive results

There is also currently no single diagnostic test that identifies allergy or indicates its severity; the only option many people have is to avoid the food completely. Business Wire describes how immunoglobulin E (IgE) epitope mapping could both identify allergies and show how severely a person might react. A precision medicine approach like this could help many people manage food allergy with less impact on daily life.

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