Food allergy is defined as an immune system response that occurs after eating certain foods. Even a tiny amount of the allergy-causing food can trigger a wide range of signs and symptoms, extending from skin rash, diarrhea, swollen airways to breathing difficulties. In some people, a food allergy can cause a life-threatening reaction known as anaphylaxis. Food allergy symptoms usually develop within a few minutes to few hours after eating the offending food. However, the onset of reactions widely varies among individuals. An oral food challenge test is a medical method for determining if a person has a specific food allergy. Under medical supervision of a specialized allergist, a suspected food will be eaten slowly, in gradually increasing amounts to accurately diagnose or rule out a true food allergy. The test provides nutritional benefits of being able to expand the diet if the food can be successfully eaten without reactions. However, if the food triggers a reaction, the benefit is knowing that the food definitely causes allergic symptoms and it must be strictly avoided to maintain good health.
Get to know “oral food challenge test”
When a food allergy develops, an immune system mistakenly identifies a specific food as a harmful substance. To respond, an immune system triggers cells to release antibodies to neutralize the allergy-causing food or food allergen.
An oral food challenge (OFC) test is a medical procedure in which suspected food is eaten slowly, in gradually increasing amounts to evaluate allergic symptoms developed after eating. An oral food challenge test is considered a highly accurate diagnostic test for food allergy. Under the medical supervision of specialized allergists, this test is the gold standard to diagnose a true food allergy and identify the threshold of responsiveness. Nonetheless, severe reactions might develop during the test, therefore to ensure the maximum level of safety while performing the test, an oral food challenge test should be conducted by specialized allergists in certified hospital with sufficient medical equipment, medical supply and medications as well as other facilities.
Common suspected foods
Foods that most commonly cause an allergic reaction are:
- Egg
- Fish
- Milk
- Soybean
- Peanut
- Wheat flour and gluten
- Shellfish and seafood e.g. shrimp, crab, shells and squid
- Tree nuts e.g. almond, walnut, cashew, macadamia and pistachio
- Certain fruits and vegetables (allergic reactions usually involve lips and lining membranes in the throat.)
Symptoms of food allergy
Food allergy is defined as an adverse immune response to food proteins or substances, resulting in a wide range of symptoms involving the dermatologic, respiratory, gastrointestinal, cardiovascular, and/or neurologic systems. Food allergy varies by type of food allergens. It can be broadly categorized into 3 main types:
- Non-IgE–Mediated Food Allergy: Non-IgE –mediated food allergy is mainly caused by a reaction involving other components of the immune system besides IgE antibodies. The allergic reactions do not usually appear immediately after the ingestion of the food allergen. Delayed symptoms usually develop several hours or even a day after food ingestion. It is usually related to skin reactions such as chronic rash and hives causing itching, redness and dry skin. In children, the most commonly affected parts are cheeks and skin folds on the feet, hands and neck. Other gastrointestinal symptoms are nausea, vomiting and bloody or severe diarrhea.
- IgE–Mediated Food Allergy: IgE–mediated food allergy is associated with more severe reactions caused by the immune response mediated through IgE antibodies. The activation of IgE and relevant immune mechanisms cause the release of histamine combined with other preformed mediators and induce rapid symptom onset, in contrast with non-IgE –mediated food allergy which is more delayed in onset. IgE –mediated food allergy encompasses a wide range of symptoms, extending from mild to severe e.g. swollen lip, swollen eye with tearing, skin rash or urticaria, respiratory problems and breathing difficulties such as wheezing, cough, chest pain and shortness of breath as well as gastrointestinal problems such as abdominal pain, nausea and vomiting. The onset of allergic reactions usually takes 30 minutes to an hour after food ingestion. IgE –mediated food allergy is a leading cause of anaphylaxis, a severe, potentially fatal allergic reaction.
- Anaphylaxis: Anaphylaxis is the most severe reaction that can potentially lead to death. Anaphylactic reactions include skin rash, hives or urticaria, red or pale skin, itching, swelling of the lips, tongue or throat, dizziness or fainting, stomach pain, vomiting or diarrhea. Severe reactions cause airway inflammation and obstruction as well as cardiovascular collapse and death.
Food allergy tests
Basic food allery tests include:
- Skin Prick Test: Skin allergy testing or skin prick test is a diagnostic test to provoke a small, controlled, allergic response of the body. During the test, the skin is exposed to suspected allergy-causing substances and is then observed for signs of an allergic reaction. To conduct this test, the patients should be healthy without taking antihistamine medications at least 1 week prior to the test. The results can be obtained in 15-20 minutes. In case that the patients had severe allergy reactions, skin prick test should be conducted a month after severe symptoms exhibited.
- Blood Test for Specific IgE: An allergen-specific IgE test measures the levels of different IgE antibodies in the blood that cause allergic reactions. Patients are not instructed to stop taking antihistamine medications prior to the test. The results can be obtained in 3-5 days. The results can be divided into 2 groups:
- Positive result: An allergist might advise the patients not to take that particular food. An oral food challenge test might be also considered (in case that the patients have had food allergy history and need to find out whether existing food allergy resolves), depending on an expert’s opinion and clinical consideration.
- Negative result: An oral food challenge test might be likely considered.
An oral food challenge is usually conducted when a careful medical history and allergy tests, such as skin prick test and blood tests are inconclusive. An oral food challenge test is a more definitive test since it apparently indicates whether the food ingested produces no symptoms or triggers a reaction.
Who should have an oral food challenge test
An oral food challenge test is highly recommended for:
- People who could safely eat certain foods in the past but were diagnosed with food allergy later. And they need to confirm for a true food allergy.
- People who were diagnosed with food allergy from blood test without symptoms.
- People who have had food allergy history and need to confirm whether food allergy is successfully treated after becoming desensitized.
- People who have suspected of food allergy with unclear symptoms.
Food allergy can develop in children due to genetic predisposition or it can also arise in adults. Food allergy can cause a wide range of allergic symptoms, extending from mild to life-threatening reactions. If severe allergic reaction exhibits, taking antihistamine medications is not advised since they might worsen the symptoms. To reduce the chance of developing serious complications, immediate medical attention provided by highly specialized allergists must be sought as soon as possible.
