What are the Different Types of Food Allergy Testing?
When a parent suspects their child might have a food allergy, they will likely want to know what types of tests may be performed to get a diagnosis. The Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary for Patients, Families, and Caregivers outlines the recommended testing in a way that makes it easy for parents to educate themselves about the various types of tests that are available. Knowing what to expect with different types of food allergy testing can ease fears and help parents to feel empowered and prepared for what lies ahead.
The role that testing plays in the diagnosis of a food allergy is often misunderstood. While testing can be a step in the pathway to diagnosis, it is not a clear indicator of a food allergy. Positive results to skin or blood tests show that your child’s body makes immunoglobulin E (IgE) antibodies to a specific food allergen but cannot be used alone to reach a diagnosis. To reach a proper diagnosis, your healthcare professional may ask a number of questions about your child’s diet history and symptoms and should use a medical history and physical exam, along with the appropriate type of food allergy testing to determine if your child’s symptoms are caused by a food allergy.
Recommended Types of Testing
Skin Prick Testing (SPT)
Skin prick tests can be conducted for specific foods and are safe and easy to perform. A skin prick test is performed by placing a drop of solution containing the expected food allergen on the child’s back or arm and then pricking that area with a small plastic probe or needle. This gently scratches or pricks the skin allowing the allergen to enter just below the skin’s surface. Results usually appear in about 30 minutes. A positive result will show a raised bump with redness around it but does not mean that your child is allergic to the food. The allergist will usually discuss the results of the SPT during the visit but may recommend additional testing or procedures prior to reaching a final diagnosis. It is important to discuss your child’s medications with the allergist prior to SPT since some medications such as antihistamines can impact results and need to be stopped several days prior to the test.
The recommended blood test for food allergy is called allergen-specific IgE (sIgE) in the serum and is performed using a blood sample from the child. This test has minimal risks and is comparative to other types of blood draws. By measuring sIgE levels, the allergist can gather information that can help identify specific foods that may be causing symptoms. This blood test may be used in addition to a skin prick test (SPT) or when an SPT is not able to be performed. Possible reasons as to why your child may need to skip the SPT could include the following: inability to stop their antihistamine medication or if extensive inflammation of the skin, such as eczema is present. Within a few days to weeks, when the blood test results are available, your allergist should discuss the results of the test and how to move forward based on the results.
Types of Tests Not Recommended
Performed by injecting a small amount of allergen into the skin with a needle, this test is not recommended because there is no evidence that has proven it to be more useful than an SPT and there is a higher possibility of an adverse reaction with intradermal testing.
Total serum IgE
Similar to the sIgE, this test is performed using a blood sample, but is unable to measure antibodies to specific foods. Instead, this test measures the total amount of IgE antibodies. There is no clinical evidence to support that this test is specific enough to provide a food allergy diagnosis.
Atopy patch test (APT)
This test is performed by placing a patch that releases a small amount of food allergen onto the skin. Research does not show that APT is helpful in diagnosing a noncontact food allergy. This test is also commonly referred to as “patch testing”.
Non-standardized & unproven tests
Listed are a few examples of tests that are not recommended for diagnosing an IgE-mediated food allergy: hair analysis, applied kinesiology, allergen-specific IgG4, and mediator release assay (LEAP diet). You can view the full list in the guidelines.
Food Elimination Diet
While elimination diets are often recommended for the management or treatment of food allergies, they can also be useful in diagnosing a food allergy, especially in the case of non-IgE-mediated or mixed IgE- and non-IgE mediated food allergy disorders such as Food Protein-Induced Enterocolitis (FPIES) and Eosinophilic Esophagitis (EoE). Your doctor should guide you on which food or foods to eliminate in your child’s diet and the amount of time your child should follow the diet. If your child’s symptoms disappear with the elimination of a food or foods from their diet, they may have a food allergy. Like the skin and blood tests, this test is also not conclusive when used alone. It is important to use elimination diets with the guidance of your health care professional since these diets can have a negative impact on your child’s nutrition intake, growth, and social/emotional wellbeing when not properly monitored.
Oral Food Challenge (OFC)
Your allergist may recommend an oral food challenge (OFC) for your child to reach a diagnosis. Since this test carries a risk of possible reaction, it is recommended to be performed in a medical facility so a healthcare professional can monitor your child and treat an allergic reaction if needed. If your child remains symptom-free after completing the OFC to a specific food, then the food that was challenged can be ruled out as a food allergen. A diagnosis will likely be confirmed by your allergist when the OFC results in symptoms that align with your child’s medical history and other test results. However, your allergist will determine the diagnosis based on information they collect while observing the OFC.
The Role of Junior Amino Acid-Based Formulas
When the use of these tests leads to a food allergy diagnosis, amino acid-based formulas can help. By providing complete nutrition, these formulas designed for children over the age of 1 year, can fill in the gaps created by elimination diets or necessary food avoidance. EquaCare Jr. provides complete nutrition at a much lower price than comparable amino acid formulas and Essential Care Jr. provides a corn and soy free option with value-added ingredients at a similar price to other amino acid-based formulas. To learn more, please visit us online or call us at 1-833-377-2773.