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Food Allergy Testing – More Questions than Answers?

If you’re working in the world of pediatric nutrition, food allergies are likely a frequent topic of conversation. And if you aren’t a peds dietitian, guaranteed you have a friend or family member who has a child with a food allergy.

The big question often is: what’s the gold standard for food allergy testing?

Before we get into the nitty gritty of allergy testing, let’s backtrack a bit and talk about the two most common categories of food allergies.

  • IgE (immunoglobulin E) mediated allergies involve reactions that are typically an acute onset, within a few minutes to 1-2 hours. These are the reactions where you’re more likely to see hives, swelling or anaphylaxis.
  • Non-IgE mediated allergies are primarily a delayed reaction in the gastrointestinal tract, but may also affect other systems of the body, and appear 2 – 72 hours after ingestion. This is where you may see blood in the stool, malabsorption or growth faltering.

In order to understand allergy testing, it’s important to understand a few key terms:

  • Sensitivity – a test’s ability to correctly identify an individual with a condition (ie. true positive)
  • Specificity – a test’s ability to correctly identify an individual without a condition (ie. true negative)

At this time, we tend to see three main types of food allergy testing completed by pediatric allergists. The first is skin prick testing, where a small amount of a food protein allergen is placed on the skin and then pricked with a needle so the body may absorb the allergen. From here, the allergist observes the skin for redness, swelling and size of the reaction if present. Skin prick testing has good sensitivity but low specificity for IgE-mediated allergies.A positive result warrants further investigation.

The second test we see utilized by allergists is serum IgE-specific tests. Here, a blood test is performed to measure the level of IgE-specific antibodies to a certain food. The higher the antibody level, the more likely it is a true positive. Like skin prick testing, serum IgE blood tests have good sensitivity but low specificity for IgE-mediated allergies.A positive result warrants further investigations.

The bottom line is that neither skin prick testing nor serum IgE-specific blood tests are diagnostic of IgE-mediated allergies.And neither test is useful for non-IgE mediated allergies.

Which brings us back to our original question – how do we accurately test for food allergies in kids? The answer is our third type of food allergy testing. Drum roll please!

The gold standard for both IgE and non-IgE mediated food allergies is a double-blinded, placebo controlled oral food challenge.Easier said than done, right? In many situations, this level of blinding is not possible, in which case a standard oral food challenge is acceptable. This involves introduction of a suspected food culprit in a medically supervised environment to monitor for appearance of symptoms.

This level of medical supervision for an oral challenge does not come without challenges. What about delayed reactions in non-IgE mediated allergies? Or how do we accommodate families who live in rural areas? Not to mention the logistics with the switch to primarily virtual visits during the COVID pandemic.

The world of food allergy testing often brings more questions than answers, but as dietitians, we are often one of the early healthcare professionals parents turn to. Understanding the ins and outs of food allergy testing is an important skill for our toolbox.

Charlene and Julie

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