The diagnosis of food allergy in adults is made with a detailed history and tests. All patients who report complaints about food are not clinically allergic to food. Food allergies can begin at any age, and many adults develop food allergies. Therefore, a detailed referral history is an essential key to diagnosis. Temporary association of symptoms related to food exposure, type and severity of reaction, response to treatment, and determination of reproducibility of the reaction are important in diagnosis. The diagnosis is confirmed by evidence of susceptibility to the culprit by a skin prick test or a serological test measuring sIgE in the blood.
Food Allergy in Adults
IgE-mediated food allergy is characterized by the immediate onset of symptoms (usually within 2 hours). Delayed reactions after ingestion may be due to food intolerances or delayed anaphylaxis such as food protein-induced enterocolitis or hives, allergy to galactose-α-1,3-galactose (α-gal) secondary to mammalian meats. Therefore, even patients who report a consistent, delayed reaction to a particular food should be referred to an allergist for evaluation. Your allergist will make the necessary evaluations for the diagnosis of food allergy in adults.
What Are Food Allergy Symptoms?
Typical food allergy symptoms indicating an IgE-mediated food allergy are characterized by their rapid onset (within 3 hours). Symptoms; urticaria, angioedema, bronchospasm, nausea, vomiting, sometimes diarrhea and, in severe cases, hypotension, unconsciousness, and dizziness due to shock (anaphylactic shock).
Many adults presenting for evaluation for possible food allergy complain of nonspecific symptoms such as bloating, changes in bowel movements, chronic abdominal pain or fatigue. These nonspecific signs are not indicative of an IgE-mediated food allergy and are often suggestive of other types of food intolerance. Some other food-related reactions, such as in food-induced enterocolitis syndrome, can cause delayed abdominal pain and vomiting to the point of severe fatigue or even drowsiness. These patients do not have other classic food allergy symptoms, such as skin or respiratory symptoms. Although food induced enterocolitis syndrome was originally thought to be a pediatric disease, it is now more commonly reported in adults, particularly crustaceans. This condition is found in patients presenting with delayed gastrointestinal symptoms, particularly seafood, and should be referred to an allergist for evaluation. Since food-induced enterocolitis is not IgE-mediated, serological tests for foods are negative.
Response to Food Allergy Treatment
It is important to know if symptoms resolve or improve with treatments such as antihistamines and whether epinephrine is needed/given. How violent was the reaction? Did it require treatment in the ER, and if so, what was it given? It is also important to know how long the symptoms last after treatment. Patients who develop severe respiratory symptoms and anaphylaxis are at higher risk of developing severe reactions again.
History of Repeat Exposure to Allergic Food
Food allergy symptoms may recur. If allergies are a concern, it is not recommended to try to eat the food again. Often, however, patients have eaten the food since the reaction and tolerated it before coming in for evaluation.
Patients do not have a classic IgE-mediated food allergy if they have consumed the same food(s) since their reaction without developing any symptoms. There are a few exceptions to this. For example, some foods are tolerated after exposure to high heat. This is most commonly seen in people who are allergic to eggs and milk but can tolerate eggs and milk in baked goods. Patients with this food allergy are sensitive to a heat-sensitive protein in milk or eggs that breaks down with baking and react only to raw and/or lightly cooked products. In pollen oral allergy syndrome, patients only react to raw fruits or vegetables and tolerate these foods in cooked or canned forms. Also, some fish allergic patients can tolerate canned fish such as canned tuna.
Some other types of food sensitivities may be due to the amount of food consumed or may be due to the co-occurrence of other factors, such as exercise in the case of food-dependent exercise-induced anaphylaxis. This is thought to be due to susceptibility to the food tolerated alone, usually wheat, to IgE. However, it causes anaphylaxis when combined with exercise or, in some cases, non-steroidal anti-inflammatory drugs or aspirin.
Allergy Tests for Diagnosing Food Allergy
The diagnosis of food allergy needs to be confirmed by evidence of susceptibility to the culprit food, either by a skin prick test or a serological test measuring serum-specific IgE. Without a supporting clinical history, these tests are not useful and should not be used to diagnose food allergy. A positive allergy test alone (skin prick test or serum-specific IgE) indicates only sensitivity, not allergy. In other words, the patient has developed antibodies but has no reaction. A greater skin prick test result or higher concentration of sIgE levels is associated with a higher probability of clinical reactions due to IgE-mediated allergy. However, none of these markers were associated with the severity of food-related allergic reactions.
There is no role for skin prick testing or food-specific IgE levels in the diagnosis of non-IgE-mediated food allergy. In case of diagnostic uncertainty, oral provocation to food(s) is required. This provocation needs to be done in a controlled environment, usually as an open food provocation.
The Importance of Molecular Allergy Testing in the Diagnosis of Food Allergy
Other laboratory tests, such as component solution diagnostic testing (molecular allergy testing), can assist in decision making and increase diagnostic accuracy. Ingredient-resolved diagnostic testing uses individual allergenic proteins in a food to identify reactivity to specific food proteins rather than the exact allergens used for standard allergy testing. Specific nutritional proteins for some foods are associated with anaphylaxis, while others are associated with pollen allergy syndrome. Adjuvant use of this modality may provide a more accurate assessment of food allergy diagnosis and exposure risks. For example, peanuts are a common food allergen in the United States, often causing life-threatening anaphylaxis. However, peanut allergy is also seen in pollen oral allergy syndrome. That’s because some of the proteins in peanuts cross-react with an allergy to birch. Allergy testing to the food component in terms of the patient’s history/food reaction may help distinguish food protein-induced enterocolitis syndrome from IgE-related peanut allergy, which can cause anaphylaxis and can be life-threatening. In the first, Ara H 8 due to pollen allergy is the protein to which patients are sensitized, anaphylaxis is associated with sensitivity to Ara H2. The serological IgE test may be positive in both cases and the diagnosis based on this may result in unnecessary food avoidance and associated emotional burdens (fear of food, fear of eating and must carry SIE).
For people with food allergy symptoms, tests such as skin food allergy test, blood food allergy test, suspending the intake of allergen foods and food loading tests should only be done by allergy specialists.
As a result;
- For the diagnosis of food allergy in adults, a detailed history is important in terms of the presence of food allergy symptoms.
- Necessary tests should be done when food allergy is suspected.
- Molecular allergy tests will be useful if there are multiple food allergies or if there is a condition such as oral allergy syndrome.
- It is very important that the diagnosis of food allergy is made by allergy specialists who have been trained in this subject.