What is a Food Challenge?
By Dan Atkins, MD
A food challenge consists of having a patient eat a food suspected of previously causing symptoms in a controlled fashion under medical supervision. The basic structure of a food challenge involves feeding gradually increasing doses of the suspected food at predetermined time intervals until symptoms occur or a normal portion of the food ingested openly is tolerated.
The history of previous suspected reactions to the food is reviewed and an interval history is taken to insure that the patient is stable. Performing a food challenge in a patient whose asthma is not well controlled is contraindicated. Obviously, a food challenge should be postponed if the child is thought to be coming down with another illness to avoid confusing results or the potential for an accelerated reaction. Vital signs, spirometry and a physical examination are performed before starting the challenge and prior to subsequent doses or whenever the patient complains of symptoms.
Food challenges come in a variety of flavors and are categorized into open, single-blind placebo-controlled or double-blind placebo-controlled depending upon who knows what the patient is receiving in each dose during the challenge.
In an open food challenge (OFC), both the patient and medical staff are aware that the patient is eating the suspected food. For example, a child receiving an OFC to egg might be given increasing doses of scrambled egg every 30 minutes until a whole egg is ingested.
In a single-blind placebo-controlled food challenge (SBPCFC) the medical staff is aware of what the patient is being fed, but the patient is not. A child receiving a SBPCFC to egg receives egg masked by concealing it in another food. The medical staff knows if and how much egg is contained in each challenge dose, but the patient and the patient's family do not. Each dose could either contain concealed egg or be a placebo. However, the final dose of any food challenge is the open ingestion of a normal portion of the suspected food. SBPCFCs are performed to eliminate bias on the part of the patient and/or the patient's family. In a double-blind placebo-controlled food challenge (DBPCFC) neither the patient nor the medical team involved in administering the challenge is aware of what the patient is being fed.
The DBPCFC is performed to eliminate both patient and observer bias. For the safety of the patient at least one physician not directly involved in the challenge must be aware of the challenge contents even in a DBPCFC. Again, the final dose of the DBPCFC is a normal portion of the suspected food ingested openly.
A food challenge is completed when the patient has an obvious reaction to the food or when a normal portion of the food has been ingested openly without symptoms. The length of time a patient is kept for observation after completion of the challenge depends upon several factors including the timing and severity of previous reactions and any concern about biphasic anaphylaxis. The results of the challenge should be thoroughly reviewed with the patient and his or her family and all questions should be addressed in light of the findings of the challenge.
