There has been a lot of questions by members of this support group on food allergy testing. I am all out for allergy testing but I should also caution that there is more that meets the eye when it comes to interpreting the results.
In my opinion, it is very important to diagnose food allergy correctly to avoid social and nutritional deficits and to ensure the safety of the patient. Mislabeling an individual with food allergy, when they are not truly allergic, can lead to nutritional deficiencies, as allergen avoidance usually includes major staple foods such as milk and egg. On the other hand, there are dangers in missing a diagnosis of food allergy because a patient who is not accurately diagnosed can have life threatening allergic reactions.
The primary tools for the diagnosis of food allergy are the medical history, possibly including food elimination diets, discriminating use of tests for food specific IgE antibodies (blood test) and oral food challenge (OFC). To date, OFC is the most definitive means of diagnosing food allergy.
Elimination diets are used to determine if a food is contributing to chronic symptoms when other testing is either not available or not suitable. In the case of breast feeding mothers, a maternal elimination diet is warranted if the baby exhibits symptoms of food allergy coinciding with consumption of the allergens in the maternal diet. In general, elimination diets should not be too long to avoid nutritional deficiencies and also to avoid a LOSS OF TOLERANCE to a food which there is IgE sensitization but no chronic disease. The loss of tolerance is something that I would like to caution mothers. I will give an example of my son’s case later on.
When starting an elimination diet, the time period is typically between a week to 6 weeks, depending on the frequency of symptoms (longer for gastrointestinal symptoms and shorter for rashes). At the end of the period, symptoms must be assessed again to see if any improvement is gained from this intervention. The diagnosis is not made by just the resolution of symptoms but also the reemergence of symptoms when the food is introduced. This is especially important in the case of atopic dermatitis as a symptom of food allergy. AD is a relapsing remitting disorder and the relapsing period may coincide with the elimination diet and therefore bias the results of the elimination and reintroduction. An elimination trial that appears to be associated with symptoms improvement should not be considered as confirmation of an allergy. Reintroducing of the food with recurrence of symptoms using an OFC should follow the elimination trial.
ORAL FOOD CHALLENGE (OFC)
Food challenges involve ingesting incremental doses of the suspected food allergen over a specific time period. Double-blind, placebo-controlled food challenge (DBPCFC) is the gold standard for diagnosis of food allergy. This involves 2 oral food challenges- one with the suspected food allergen and one with a placebo food. Both the patient and the challenger are blind to which food products contain which to eliminate bias. This type of challenge is usually done in a research setting.
Determining WHEN to challenge is also important:
- patient’s age
- history of reactivity to the food
- medical history
- food specific IgE measurements
- other food allergies