Two years ago, a typical breakfast outing with my family changed our lives. My six-month-old showed interest in my scrambled eggs, so I gave him a few spoonfuls. By the time we got home ten minutes later, his face was red and hives were popping up across his face. After a visit to pediatric urgent care, we soon found ourselves researching local pediatric allergists. But getting a proper food allergy diagnosis took several visits and different types of allergy tests. Over the next two years, we learned he was allergic to eggs, cashews, and pistachios.
According to the American College of Allergy, Asthma and Immunology (ACAAI), food allergies affect an estimated four to six percent of children and four percent of adults. For these families, the path from testing to diagnosis can feel daunting and overwhelming. In this post, I’ll break down the different types of food allergy testing methods and what to expect from a food allergy diagnosis.
What happens when you have a food allergy?
Your body’s immune system makes a particular kind of antibody called Immunoglobulin E (IgE) to protect you from pathogens. Your body isn’t supposed to trigger an immune response to proteins in your environment. But if you have an allergy, your body produces IgE antibodies in response to the presence of your allergen, a substance that is otherwise harmless to everyone else. When you have a food allergy and you consume or, in some cases, come in close contact with your allergen, your IgE antibodies bind to the allergen. When this binding happens, a number of reactions are triggered in your body, including releasing histamine into your bloodstream. While there are many different types of food allergens, some examples include peanuts, soy, dairy and egg.
Histamine is responsible for the symptoms of your allergic reaction. These symptoms can range from mild to severe, including hives, rash, shortness of breath and vomiting. In severe cases, the body can experience something called anaphylaxis or, worse, anaphylactic shock, in which your body goes into shock and you can even stop breathing. Fortunately, deadly reactions are very rare. And anaphylaxis can usually be stopped with a properly timed shot of epinephrine.
Should I have my child tested?
If you’ve seen your child react to one or more foods with any of the symptoms described above, the next step is to make an appointment with your doctor or pediatric allergist to determine the best testing options. While you’re waiting to undergo testing, it’s best to avoid the suspected allergen altogether.
To avoid false positives, allergy testing should only be pursued after an observed reaction. In a 2016 study conducted by Dr. Ruchi Gupta, MD, MPH, who has previously spoken with SciMoms about food allergies, 53 percent of siblings of food allergy patients tested positive for food allergies using the skin prick method when, in actuality, they had no symptoms of a food allergy.
Should I talk to my pediatrician or a pediatric allergist?
Many pediatricians will refer you to an allergist or immunologist for testing and treatment. These specialists get two years of additional training focused on diagnosing and treating allergic/immunologic disorders. You also have the option of finding board-certified allergists and immunologists, who must pass a special certification exam to demonstrate their expertise and also regularly undergo continuing education to stay updated on the latest testing and treatment standards. With their specialized training in the latest guidelines and best practices, an allergy specialist or board-certified allergist can help reduce unnecessary testing and misinterpretation of test results, according to one 2016 study published in Pediatrics.
How are food allergies diagnosed?
There are three types of tests used in food allergy diagnosis: food challenge, skin, and blood tests, but the food challenge test is the only one that provides a definitive diagnosis. In 2010, the National Institute of Allergy and Infectious Diseases published an extensive set of proper food allergy diagnosis guidelines. According to these guidelines, healthcare providers should use a combination of clues from the patient’s medical history, a physical exam, and one or more forms of testing in order to make a diagnosis.
Physician-supervised oral food challenges are the only tests that can truly diagnose a food allergy and are therefore considered the “gold standard.” However, skin puncture tests and bloodwork can also be used to help identify foods causing allergic reactions. These tests work by testing for IgE antibodies, though neither test on their own enables a true diagnosis.
Food hypersensitivities, such as eosinophilic esophagitis and food protein-induced enterocolitis syndrome (FPIES), are food allergies mediated by the immune system that do not involve IgE antibodies, and are therefore best diagnosed with a combination of elimination diets and food oral challenges. Symptoms are largely gastrointestinal in nature and typically occur several hours after ingestion of a food. While these are often thought to be less life threatening, they can cause severe dehydration.
A closer look at each type of test
How it’s done: For this test, the patient is fed increasing doses of the suspected allergen under medical supervision over the course of a few hours to see if they have a reaction.
What you need to know: This test is the “gold standard” because it is the only method that gives a truly accurate result and a definitive diagnosis. Challenges are often used to determine if a food allergy has been outgrown.
Interpretation of results: If the patient gets through the whole challenge without reacting, they aren’t allergic. If the patient does react, then the allergy is confirmed.
How it’s done: For this test, a small amount of the suspected food allergen is placed on the patient’s forearm or back. The allergist then pricks the skin with a small needle to let a tiny amount of the allergen get beneath the skin.
What you need to know: Skin tests are the most common form of allergy testing. The test is cost-effective and results can be obtained quickly, usually in just 30 minutes. This test is NOT recommended, however, if the patient has severe eczema since the condition’s inflammation makes the skin-prick test challenging to interpret.
Interpretation of results: If a “wheal,” a type of hive, forms at the site where the allergen is tested that is bigger than the no-allergen site on the skin, that indicates a positive test result. These tests are often used to help inform your doctor’s diagnosis, but remember that a positive skin-prick test alone is not enough to confirm a food allergy due to high false positives rates. This can be particularly true for food allergens because the test does not mimic how your body encounters the digested allergen.
How it’s done: For these tests, blood is drawn from the patient and tested for the presence of antibodies (IgE) specific to the suspected allergen.
What you need to know: Allergen-specific blood tests are considered as an alternative to skin-prick tests for patients who can not stop taking antihistamines for testing purposes or if there is a concern for a severe reaction from exposure to the allergen. This test may also be done in addition to skin-prick tests, especially if those results were inconclusive.
Interpretation of results: How well the results predict whether a food allergy exists is unique to every food; however, the higher the levels of IgE recorded in the blood, the more likely you are to have an IgE-mediated allergy. If antibodies are not present, it’s unlikely the patient is allergic. Like skin-prick tests, however, this test alone can not confirm the food allergy due to the risk of false positives. To make matters more confusing, labs sometimes categorize results into qualitative levels with no clinical meaning, such as “low,” “moderate,” “high,” and “very high,” even though there is no evidence that high IgE levels correlate to a more severe reaction. In some cases, an elevated IgE level might even be observed when the patient shows no physical symptoms when exposed.
In our own diagnosis journey, we experienced first-hand how skin-prick tests and blood tests can be misleading. My son’s skin-prick tests showed positive results for cashews, pistachios, walnuts, pecans, and hazelnuts even though he had eaten and tolerated walnuts, pecans, and hazelnuts prior to testing without any trouble. Had we done the skin-prick tests before exposing him to those tree nuts, or without a food challenge, we might have eliminated those valuable sources of nutrients from his diet unnecessarily.
What tests to avoid
You may have heard or seen advertisements for food allergy test methods like hair analysis testing and applied kinesiology offered by some alternative practitioners. There has been no scientific verification for many of these alternative tests. Some may even be dangerous if you are allergic to the suspected food. You should also avoid direct-to-consumer food allergy testing kits and food sensitivity tests, as these are marketed for testing sensitivities rather than true allergies and are not scientifically validated for either. There is also no genetic test for allergies.
Life after a food allergy diagnosis
Receiving a food allergy diagnosis can feel overwhelming, but your allergist can help your family learn how to navigate the ins and outs of living with a food allergy.
Your first step is to learn to read food labels to avoid your child’s allergen. Your allergist will typically provide you with this information, but a registered dietitian can also help you find good food substitutes.
Food labels can be confusing. Keep the following in mind:
- By law, the top eight food allergens (milk, egg, peanut, tree nuts, soy, wheat, fish, and crustacean shellfish) must be included on ingredient lists by using the allergen’s common name, indicating the word “contains” followed by the name of the major food allergen, or in parentheses when the ingredient is a less common form of the allergen, for example, “albumin (egg).”
- If you have a less common food allergy, you’ll need to become familiar with the alternative names for your allergen so you can spot it on the label.
- Some foods and beverages are exempt from these labeling requirements, including meat, poultry, certain egg products, distilled spirits, wine, and beer. Cosmetics, shampoos, and other health and beauty aids are also exempt.
- Manufacturers also aren’t required to indicate whether their products are made on equipment or in a facility that makes other food products containing one of the top eight allergens. Some manufacturers will include a cross-contamination warning voluntarily, but these warnings vary widely because there is no regulatory standard. If you are unsure about whether a product could have come in contact with an allergen, contact the manufacturer directly for more information. You should also consult with your allergist to develop an approach to food labels that works for you and your family.
Another important step is preparing an emergency care plan with your physician to share with everyone who cares for your child. Your doctor will help you outline under what circumstances antihistamines can be administered and when epinephrine or emergency care is required. The plan should also outline the proper dosage of the recommended medications, additional emergency contacts and instructions, such as the preferred hospital for treatment.
Last but not least, it is critical to learn how to use epinephrine auto-injectors.
Bottom line: knowledge is power
Food allergies can be stressful. Because food is at the heart of many family and cultural traditions, it can feel isolating when you or your child can’t eat something on the menu. But research efforts are underway to help us better understand food allergies and develop improved diagnostic procedures and new treatment options. In recent years, education and policy initiatives have also helped bring more public attention to food allergies. With time and practice, you can become more confident in managing your food allergy.
Leidamarie Tirado-Lee is a scientist with training spanning molecular biology and bioengineering. While pursuing her PhD at Northwestern University, she began blogging for the university’s Helix Magazine and discovered a passion for communicating the wonders of science through the power of the written word. Some of her blogs have been covered by Nature Chemistry Blogroll and Mashed.com. She now works as a science communicator in the biotech industry. Outside of science, Leidamarie is the mom of an energetic and curious toddler.