Food Allergy Testing
The history of exposure to an allergenic food is the most important part of the evaluation for a food allergy. If your child has a history of symptoms after eating an allergenic food, then there are 3 different tests that your allergist may recommend:
Skin Prick Testing: In this test, a tiny amount of allergen will be introduced through the top layer into the second layer.
Specific IgE Blood Testing: This test measures the levels of IgE that are present in the blood to a specific allergen. Like the skin prick test, it has a high negative predictive value, which means a negative result is most likely accurate. But it has a low positive predictive value, which again means there’s a greater chance of getting a false positive result. If high levels of specific IgE are seen, then a food allergy may be diagnosed.
An important note about Skin Prick Testing and Blood Testing: Remember, blood and skin tests alone cannot be used to diagnose food allergy. A person does not have a food allergy unless they also have clinical symptoms. There is also a chance that a person could have a "false positive" on their skin or blood test -- about 50% of people who have a "positive" (allergic) response to a skin prick test can eat the food without any clinical problems.
Oral Food Challenge: Exposes a person to their potential allergenic food in small doses, slowly increasing over time with careful observation in a medical facility to watch for signs of an allergic reaction. An oral food challenge is the only way to definitively diagnose a food allergy.
The only way to definitely diagnose a food allergy is with an oral food challenge.
However, oral food challenges can make patients and parents anxious, thus many times they are avoided and a diagnosis is made based on the other tests above plus the person’s medical history. A patient’s medical history (their reported experiences after exposure to the specific food) is the most important part of the evaluation for a food allergy diagnosis.
Allergy Trends
Food Allergies Are On the Rise
Food allergies are on the rise and have reached epidemic proportions, with 32 million, or more than 1 in 10 in the US, now suffering from a food allergy. Not only are food allergies inconvenient for families to manage, but one accidental exposure can have potentially life-threatening consequences. In fact, more than 40% of food allergic children have experienced a severe reaction.
Top 9 Allergens
Although more than 170 foods have been identified as triggers of food allergy, the FDA classifies 9 foods/food groups as the major food allergens in the US:
milk, egg, peanut, tree nuts, shellfish, fish, wheat, soy and sesame.
In young children, milk, egg, and peanut comprise > 80% of food allergies.
Not only do these represent the most common childhood food allergies, but studies indicate that with early introduction, there can be a significant reduction in the development of an allergy to these foods.
Top Allergens: Key Trends and Facts
Egg
- Affects 2% of children 3
- Usually presents in the 1st year of life
- ~ 30% of children do not “outgrow” (or become tolerant to) their egg allergy, which often happens as late as teenage years
Milk
- Most common food allergy in infants and young children
- Affects 2-3% of children < 3 years old 4
- Usually presents in 1st year of life
- Though most children “outgrow” (or become tolerant to) their milk allergy, it remains the most common cause of reactions in school
Peanut
- Affects up to 2.5% of children 5
- Peanut allergy is more likely to be lifelong; only 20% outgrow a peanut allergy
- Although peanut is the allergen most often associated with severe or fatal reactions, any food allergen has the potential to cause anaphylaxis
Shellfish
- Affects 1-1.5% of children 6
- Includes shrimp, lobster, squid, crab, scallops
- Often caused by a protein called tropomyosin
- Even the steam from cooking can trigger an allergy
Fish
- Affects 0.5% of children 6
- Up to 40% of fish allergies develop in adulthood
- May be allergic to finned fish and not shellfish or vice versa
Soy
- Affects 0.4% of children, normally under the age of 3; affects 0.3% of the general population 6
- 70% outgrow it by age 10
- Found in many food products, so it’s important to read the labels
Wheat
- Affects 0.4% of children 6
- Often outgrown by 10 years of age
- Not to be confused with celiac disease. People with a wheat allergy can often have other grains that are not wheat
- Wheat is sometimes found in cosmetic products. People with wheat allergies should avoid using these products on their body
Tree Nuts
- Affects 1% of the general population 7
- Many people with tree nut allergies are only allergic to 1 or 2 types of tree nuts. Therefore, it’s worth working with an allergist to determine if they can safely eat other types of tree nuts
- Includes brazil nuts, cashews, pistachios, almonds, macadamia nuts, walnuts, pine nuts (as well as foods made with these nuts)
Sesame
- Affects 1 million children and adults 8
- Most often develops in children, but can develop at any age
- Designated as ninth top allergen, with the 2021 FASTER Act