When it comes to diagnosing food allergies, there are two tests that healthcare providers typically turn to: skin-prick testing and specific IgE (sIgE) blood testing. On the surface, both seem fairly simple. But have you ever wondered what these tests are actually measuring and how exactly they aid in the diagnosis of a food allergy?
Well, you’ve come to the right place. Refresh your beverage, log out of Twitter, and settle in as we present a deep dive into the science behind allergy diagnostics. Things might get a little bit complicated, but we promise we’ll make the ride as smooth as possible.
We’re going to let you in on a secret: To really understand allergies and how they are diagnosed, we need to discuss the immune system. Yep. That immune system. The one you use to fight colds, flus, and everything in between.
Let’s start with something called Immunoglobulin E (IgE).
What is IgE?
Our immune systems contain a complicated network of defenders that work together to keep us healthy. Some of those defenders are called immunoglobulins, aka antibodies, which bind to pathogens such as viruses and microbes to disable them. You have probably heard of these little guys in relation to the common cold or infections that your body fends off. The same sort of army of defenders is called up to deal with allergic triggers.
Allergies happen when our bodies produce elevated levels of a certain type of antibody defender, called IgE, to fight off the perceived threat of an allergen.
We’re getting ahead of ourselves. Time for a quick history lesson.
IgE was discovered in 1967 when researchers found that people who had allergic reactions to substances that were not typically harmful (think pollen or milk) had elevated levels of specific IgE antibodies in their blood.1 The symptoms of an allergic reaction are triggered when the IgE antibodies interact with an allergen and signal the release of chemicals, including histamine. This dangerous dance can lead to everything from hives and itchy eyes to anaphylaxis.
What is allergic sensitization?
People who produce elevated sIgE that can recognize a specific allergen are described as being “sensitized” to the allergen. Having an increase in sIgE is correlated with an increased likelihood of having an allergic reaction when exposed to that allergen.
But sensitization doesn’t guarantee that the person will definitely have an allergic reaction. In the case of food allergies, it also doesn’t indicate that a food should be completely removed from a patient’s diet, especially if the patient is currently eating the allergen without problems.
At the molecular level, IgE antibodies don’t actually react to whole foods. There is no alarm screen that says “WARNING: PEANUT” or “INTRUDER DETECTED: EGG.” Instead, IgE antibodies are recognizing and interacting with small fragments of each allergen. In the diagnostic world, these fragments are called allergen components.
What are allergen components?
Let’s think of a whole allergen, such as a peanut, as a big puzzle. Each piece of the puzzle is usually a small part of a protein that could be recognized by an IgE antibody. We call these different puzzle pieces “components” and the diagnostic tests that recognize them “component tests.” In most cases, a specific allergen component binds to the IgE antibody that recognizes it and not any others, similar to a key fitting into a lock.