Food Allergies: Why A Food Challenge Is Very Often Helpful

Robert Winkler Robert Winkler

Has your child recently been tested positive for food allergies? Are you in doubt or get conflicting or even contradictive information about your child`s allergy? Then you should know about the “food challenge test” -it may help you clarify what is actually going on….


Food allergies are still a major problem in everyday practice.  In fact, it seems that the numbers are still rising in many countries of the world. The overall prevalence of food allergy in children is estimated to be between 8 and 10%. In adults, the numbers are somehow smaller-being due to the fact that many children actually  outgrow their food allergy. However,it is important to remember  these allergies  can appear at any age. The main problem is a correct diagnosis.

How do doctors diagnose a food allergy?

As we already discussed in our latest blog, allergy testing is a bit of an art and requires a lot of expertise. Allergy  tests should be preformed by doctors who underwent specialist allergy training to begin with.  Do not trust unproven or unscientific tests-they can be very dangerous.  There are a variety of reliable skin test and also blood tests available. What is sometimes difficult to understand-these tests  do NOT measure “allergy yes or no”- they prove ‘sensitization”.  What does that mean?  Well, basically it  means the immune system has had contact with the allergen and is ‘alert”- that is very different from an actual allergy!!  The interpretation of these tests is therefore not as easy as it may seem- a positive test result does not always equal clinically relevant allergy! This is even more  true for food allergies!  Eventually this means there are a lot of children (and adults) who are put on (sometimes harmful) diets-for no reason at all.

This is the reasons that  doctors sometimes need to perform a  so called challenge test (this test is also called provocation test). It is the one test that “proves ” the allergen is truly responsible for your child`s symptoms. 

What exactly is a food challenge? An oral food challenge (OFC) is a medical procedure in which a certain food -that is suspected to be responsible for your child`s  symptoms-  is eaten , in gradually increasing amounts, under medical supervision. As an example, a child is asked to eat a tiny piece of a peanut (or the peanut  is mixed in a cookie)-then the amount is roughly doubled every 20-30minutes until the full dose is reached.

When will an open food challenge (OFC) be performed?

As mentioned above , OFCs are usually done when   allergy tests, such as skin and blood tests, are inconclusive. The OFC is a more reliable  test because it will show whether the food actually  produces symptoms or triggers a reaction.  It has also been called the “gold standard” of food allergy testing.

What are the benefits of a Food challenge? The main benefits include the nutritional ( and social! ) benefits of being able to tolerate  the diet if the food is successfully eaten without causing any issues. The reality is that there are a lot of children – and adults too- out there who have been put on a diet that may actually cause more harm than good!  However, even if the food did trigger  a clinical reaction, the benefit is knowing that the food is actually a problem. It will reassure the patient (and/or the parents) that this food is truly a problem and needs to be avoided in order to prevent acute or chronic health issues. It does NOT mean the food needs to be avoided for ever!! If more than 1 food are suspected, different food challenges – at different times- need to be arranged.

What are the OFC risks? The risks of OFC include an allergic reaction including anaphylaxis. There is no evidence that having an allergic reaction during an OFC makes future reactions worse or prolongs allergy in children.  

What is important to know before doing a food challenge?

Patients should be in good health, for example  if they have an acute infection the test cannot be performed. The food in question should be avoided at least 2 weeks-if it isn`t avoided anyway. Other  allergic conditions such as asthma, eczema and hay fever should be under control- meaning not cause significant clinical symptoms so they can`t be misinterpreted as symptoms of a positive test.  

Is it necessary to  stop the  usual antiallergic medication before the test?

Yes. This is especially true for antihistamines. They might mask mild early symptoms of a positive challenge

What exactly happens during a test?

Usually the children can have a light meal, for example breakfast, at home, before starting the test. A doctor will perform a physical examination and vital signs are done before starting and periodically during the test. The OFC starts with a small serving of the food and after a period of time, usually 15-30 minutes, if no symptoms are present, a slightly larger amount is eaten. The total duration of the test can vary, obviously the test needs to be stopped once a “true” allergic reaction is suspected. There are clear “stop criteria” that are taught to the nurses performing the test.  In a best case scenario, the test can take up to 3-4 hours until a “normal” serving of the food in question has been eaten and tolerated.

What happens if a true allergic reaction happens during the test?

Most food challenges that result in a reaction will trigger skin or stomach symptoms. The symptoms are usually mild because the testing is done gradually with small amounts of food at the start, and feeding is stopped at the onset of symptoms. Most often, antihistamines are given for these mild symptoms. In rare cases, the symptoms can be more severe and medications such as adrenaline may be needed.

How long do patients have to stay in the hospital after the test? If there were no symptoms during an OFC, usually patients are discharged from the hospital or office  within 1 to 3 hours. In case of allergic symptoms, the patient is typically watched for at least 2 to 4 hours from the time symptoms go away or improve, with longer observation periods required for patients with more severe reactions.

Can food challenges be done at home?

The overall recommendation is NOT to perform a food challenge at home! The main reason is simply safety!  However there may well be cases when small amounts of the food have already been tolerated in processed forms. A good example would be cookies containing milk protein. Some people do actually try a stepwise approach such as the “milk ladder” or the “egg ladder”. It cannot be overemphasized that such an approach MUST be approved by the allergist and parents need to be trained in emergency medication.

 

References

1.EAACI Food allergy and anaphylaxis guidelines

2. ASCIA Info on Food allergy challenges 2017, www.allergy.org.au

3.Boyce JA, Assa'ad A, Burks AW, et al. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Summary of the NIAID-Sponsored Expert Panel Report. J Allergy Clin Immunol 2010;126:1105-18. 4. Sampson HA, Aceves S, Bock SA, et al. Food allergy: A practice parameter update-2014. J Allergy Clin Immunol 2014. 5. Nowak-Wegrzyn A, Assa'ad AH, Bahna SL, et al. Work Group report: oral food challenge testing. J Allergy Clin Immunol 2009;123:S365-83.