First developed by English physician Charles Blackley in 1872, the concept of allergy testing has been around for longer than many might think. However, since Blackley’s experiments, food allergy testing has evolved significantly, particularly with the introduction of total and specific immunoglobulin E (IgE) tests. Following the discovery of IgE as the immunoglobulin responsible for type 1 hypersensitivity reactions in 1967, allergy testing has only become more specific, offering deeper essential insights into a person’s diagnosis and treatment plan.  

Food allergies are increasingly common, and according to the U.S. Centers for Disease Control and Prevention (CDC), the prevalence of food allergies has increased by 50% since the 1990s, making it a serious public health concern. 

Innovations like Xolair, an FDA-approved injectable medication intended to reduce allergic reactions caused by accidental exposure to food triggers, are promising for those with allergies. However, early and accurate diagnosis remains the cornerstone of effective management and prevention of allergic reactions.

Although allergy testing has evolved substantially since Blackley’s work, the fundamental reason remains unchanged: patients still require accurate, validated testing to be able to determine the root cause of symptoms, enabling them to work with their healthcare team to create effective management plans. 

The state of food allergy testing 

Advances in allergy diagnostics are making it easier for clinicians to identify not only the specific allergens that may be responsible for patients’ symptoms, but also how specific sensitization patterns may help to predict both severity and risk involved with allergic disorders. In turn, this allows for more precise treatment and management advice for both primary care and specialist clinicians alike.

What many might not realize is that the most important ‘test’ is actually a patients’ clinical history. A thorough history is critical, as blood testing and skin prick testing don’t necessarily indicate a clinical allergy, but rather sensitization to an allergen. For a patient to have a clinical allergy, they must have symptoms upon exposure to food as well as sensitization.

The proper gathering of a patient’s history should include an assessment of symptoms consistent with IgE mediated food allergy, which may involve the skin, gastrointestinal tract, cardiovascular system, or respiratory tract, coupled with timing following food ingestion, with the exception of specific delayed reactions. Reactions also should be consistently reproducible, and the form of the food ingested should also be considered. For example, certain foods like milk might cause an allergic reaction when consumed fresh but not when baked. 

In addition to patient history, the three validated testing options include blood tests, skin-prick tests (SPT), and food challenge tests. The first, IgE blood testing, is quick and safe, as there’s no chance of triggering an allergic reaction and may be ordered by any clinician that normally orders laboratory testing. Detailed results from these tests show the levels of allergen-specific IgE antibodies in blood and can reveal sensitization from among a selection of hundreds of possible allergens. 

There are two types of IgE blood testing: whole allergen and allergen component. Whereas whole allergen testing helps identify potential allergic triggers and confirm or rule out allergies, the allergen component tests focus on pinpointing specific proteins in an allergen that may be responsible for triggering symptoms. Testing for allergen components adds to the specificity of a patient’s diagnosis and also helps identify irrelevant cross-reactivity. 

For instance, patients who have a tree pollen respiratory allergy and a positive blood test to peanuts may be reacting to a protein in the peanut that is similar to tree pollen. Sensitization to only this specific protein is an indication that they may have either no symptoms or mild symptoms when ingesting peanuts. This insight allows clinicians to be more specific in their diagnosis and more precise in their management recommendations. Certain proteins in milk and eggs may help to indicate which patients may tolerate baked but not fresh forms of the food as mentioned earlier.

The second validated testing option, SPTs, are fast, with results often obtained in less than an hour, and involve skin being directly exposed to suspected allergens and observed for any signs of a reaction. Food challenge tests, also known as oral food challenges, are also extremely useful when leveraged alongside a blood test or SPT to confirm an allergy or determine if a patient has even outgrown an allergy. 

However, while both blood tests and SPTs are effective diagnostic tools, specific IgE blood tests have certain benefits over SPTs, including no risk of anaphylaxis or skin pigmentation/ condition on test results, and no limitations on medications like antihistamines prior to testing. 

Controversial and evolving allergy testing methods

When discussing the industry standard for food allergy diagnostic tools, it’s also important to point out the allergy testing methods that are still unproven, as well as those that are evolving and show potential but have not yet been widely adopted in clinical practice. 

Firstly, there are two kinds of testing that are commonly referenced but are ultimately unproven: specific Immunoglobulin G (IgG) tests and hair analysis. While the first method, IgG testing, can determine the concentration of circulating allergen-specific IgG antibodies in human serum or plasma, these antibodies are part of the natural defense system of the body and develop in response to contact with foreign substances. For food allergies, it’s important to understand that IgG testing is an unproven method for diagnosing allergy, and in fact, higher levels of IgG might actually be associated with tolerance to food. Another method, hair analysis, is also unproven as a tool for allergy testing and can result in misdiagnosis, as well as costly, unnecessary dietary restrictions and other potential health risks for patients. Additional unproven diagnostic approaches include cytotoxic testing, electrodermal testing, and iridology. 

On the other hand, evolving testing methods include Basophil Activation Testing (BAT) and epitope pattern analysis. While neither of these methods are currently FDA cleared or readily available in a community setting, both forms of testing might have a role in diagnosing food allergies in the future as research evolves.

Why the right diagnostic approach matters

Getting the correct food allergy diagnosis leads to increased diet diversity and potentially improved nutrition when suspected allergies are ruled out, making it critical to take the right diagnostic approach from the beginning. Additionally, improving diagnostic specificity also means that clinicians may be able to perform fewer higher risk oral food challenges and potentially more lower risk food challenges helping to get an increased number of patients to an accurate diagnosis. By taking the right diagnostic approach, this ultimately shifts allergy management from reactive to proactive, ensuring better care and improved quality of life for patients.

Photo: Sean Gallup, Getty Images

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