Oral food challenge

OFCs can be used to diagnose food allergies, determine tolerance development, and evaluate tolerance of cross-reactive foods.^[2][3] In Japan, OFCs are also used to find out how much of a food allergen a person can safely eat before having a reaction.^[2]

OFCs are the main method for diagnosing food allergies.^[2] They are usually performed if skin prick tests and allergy blood tests are inconclusive for IgE-mediated food allergies, which involve rapid allergic reactions triggered by IgE antibodies.^[1] Newer tests, including component-resolved diagnostics (CRD) and basophil activation tests (BAT), were also created as safer alternatives because they do not require oral intake of possible food allergens and can be informative of reaction severity.^[2] Component-resolved diagnostics evaluates an individual’s blood to measure IgE sensitivity to purified native or recombinant allergens.^[4] A basophil activation test evaluates an individual’s blood by measuring how basophils respond after the cells are exposed to specific allergens.^[5] However, CRD and BAT may not be readily available in all clinical settings and may provide unclear results.^[2]

OFCs can also be used to confirm the diagnosis of food protein-induced enterocolitis syndrome (FPIES) and determine whether tolerance has developed. FPIES is a non-immunoglobulin E (IgE)-mediated food allergy that occurs most commonly in infants.^[6] It causes delayed vomiting about 1 to 4 hours after eating the allergen.^[7] Tolerance is typically evaluated around 12 to 18 months following the last reaction. The timing of an OFC depends on several factors, including the type of food, its importance in the child’s diet, and the severity of previous reactions. Unlike IgE-mediated food allergies, FPIES presents with delayed allergic reactions, so patients are given the lowest dosage that is most likely to cause a reaction rather than gradually increasing amounts.^[6]

During an OFC, most patients only have minimal reactions, such as hives or skin irritation. Serious allergic reactions are uncommon but may include anaphylaxis and trouble breathing. When severe reactions occur, healthcare providers are prepared to provide fast treatment, including administration of epinephrine. As such, OFCs should only be performed in a hospital or clinical setting to ensure patient safety.^[1]

A positive OFC indicates that the patient should avoid eating the food allergen to prevent an allergic reaction. If patients successfully pass their OFC without any symptoms, they can safely reintroduce the food into their diet.^[1]

There are different types of oral food challenges:^[1][8]

• Double-blind, placebo-controlled
  • This is the gold standard method that is most used in research studies rather than routine clinical practice.
  • Neither the allergist nor the patient knows which food portion contains the allergen and which is the placebo. The allergen-containing food and the placebo are given separately, typically hours or days apart.
• Single blind
  • Only the allergist knows which food portion contains the allergen and which is the placebo. The allergen-containing food and the placebo are given separately, typically hours or days apart.
• Open food
  • This is the most common type of oral food challenge used in clinical practice.
  • Both the allergist and patient know that the allergen is being eaten. The food is given in gradually increasing portions over an hour.

Before a double-blind, placebo-controlled oral food challenge, patients are instructed to avoid the test food for at least two weeks. The challenge is usually done on an empty stomach, so patients are told to not eat for 2 to 4 hours before the test.

The challenge should be rescheduled if a patient has an uncontrolled or worsening medical condition, such as asthma, atopic dermatitis, or an acute infection, depending on the physician’s judgment. If these atopic conditions are chronic and well-controlled, physicians may proceed with the challenge. However, physicians should explain the limitations of interpreting the results from the OFC if patients are presently having baseline symptoms of redness, itchiness, and more due to their preexisting medical condition. OFCs should not be completed if patients have chronic medical conditions that could increase the risk of complications if anaphylaxis occurs or if treatment is required. Medical conditions that can increase the risk of complications during treatment of an allergic reaction include heart disease, chronic lung disease, and pregnancy.

Medications such as antihistamines, bronchodilators, and anti-IgE monoclonal antibodies may affect OFC results because they can reduce or change the symptoms of an allergic reaction.^[9]