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Food Allergy Test – Methods and Diagnosis

A food allergy test helps identify allergic reactions and sensitivities to specific foods. It is used by doctors to provide targeted dietary recommendations and treatment plans.

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Things worth knowing about "Food Allergy Test"

A food allergy test helps identify allergic reactions and sensitivities to specific foods. It is used by doctors to provide targeted dietary recommendations and treatment plans.

What Is a Food Allergy Test?

A food allergy test is a diagnostic procedure used to determine whether a person´s immune system reacts abnormally to specific foods or food components. In a true food allergy, the immune system mistakenly identifies harmless food proteins as threats and produces antibodies against them. This can lead to a wide range of symptoms, from mild skin reactions to severe anaphylactic shock.

Food allergy tests are typically performed by allergists or immunologists and form a key part of allergological diagnosis.

Types of Food Allergy Tests

Skin Prick Test

In the skin prick test, small amounts of standardized food allergen extracts are applied to the skin, usually on the forearm or back, and a fine lancet is used to lightly prick the skin through each drop. After approximately 15 to 20 minutes, the site is assessed for the formation of a wheal (raised bump) or redness, which indicates sensitization to the allergen.

Specific IgE Blood Test (RAST / ImmunoCAP)

The specific IgE blood test involves taking a blood sample and analyzing it in a laboratory for the presence of immunoglobulin E (IgE) antibodies directed against specific food allergens. This test is particularly suitable for individuals taking medications that could interfere with skin testing (such as antihistamines), or for those in whom skin testing is not feasible. Commonly used methods include the RAST test and the more modern ImmunoCAP test.

Patch Test (Epicutaneous Test)

The patch test is primarily used when a delayed allergic reaction (Type IV allergy) is suspected. Suspected allergens are applied to adhesive patches placed on the back and left in place for 48 hours. Results are evaluated at 48 and 72 hours after application.

Oral Food Challenge

The oral food challenge (OFC) is considered the gold standard in food allergy diagnosis. Under medical supervision, the patient consumes increasing amounts of the suspected food. There are two main types:

Open food challenge: Both the patient and the doctor know which food is being tested.
Double-blind placebo-controlled food challenge (DBPCFC): Neither the patient nor the doctor knows whether the real allergen or a placebo is being administered. This is the most reliable method for confirming a food allergy diagnosis.

When Is a Food Allergy Test Recommended?

A food allergy test is recommended when the following symptoms occur after eating:

Hives (urticaria) or skin redness
Swelling of the lips, tongue, or throat (angioedema)
Itching in the mouth or throat (oral allergy syndrome)
Gastrointestinal complaints such as nausea, vomiting, or diarrhea
Respiratory symptoms such as coughing, wheezing, or shortness of breath
Severe reactions including anaphylactic shock

Among the most commonly tested food allergens are peanuts, tree nuts (e.g., hazelnuts, walnuts), cow´s milk, hen´s eggs, wheat, soy, fish, and shellfish.

Procedure and Preparation

Before undergoing a food allergy test, it is important to inform the doctor about all current medications, as certain drugs such as antihistamines or corticosteroids can interfere with test results. Depending on the test method, these medications may need to be paused for several days beforehand. For oral food challenges, a prior elimination diet (avoiding the suspected food) is often required.

Validity and Limitations

No single test is sufficient on its own to reliably diagnose a food allergy. The results of skin and blood tests only indicate sensitization, meaning the presence of antibodies, which does not necessarily mean clinical symptoms will occur. A reliable diagnosis can only be made by combining test results with a thorough medical history (anamnesis) and an oral food challenge.

It is important to note that commercial self-tests (such as IgG-based tests available online) are explicitly not recommended by professional organizations such as the European Academy of Allergy and Clinical Immunology (EAACI), as they do not provide a valid basis for diagnosing food allergies.

Treatment After Diagnosis

Once a food allergy has been diagnosed, management typically includes:

Allergen avoidance: Strict elimination of the offending food from the diet
Emergency medication: Carrying an epinephrine auto-injector (e.g., EpiPen) for severe allergies
Oral immunotherapy (OIT): Gradual, controlled exposure to the allergen under medical supervision, for example in peanut allergy
Nutritional counseling: Support in creating a safe, allergen-free meal plan

References

Muraro A. et al.: EAACI Food Allergy and Anaphylaxis Guidelines: diagnosis and management of food allergy. Allergy, 2014; 69(8): 1008-1025.
World Allergy Organization (WAO): White Book on Allergy, 2013 Update. Available at: www.worldallergy.org
Sampson H.A. et al.: Food allergy: A practice parameter update -- 2014. Journal of Allergy and Clinical Immunology, 2014; 134(5): 1016-1025.

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