Allergy Challenge

Like all medical tests, allergy tests have their drawbacks and are not perfect. Skin prick testing and blood tests are not always correct, particularly in food allergy, so the only way to be certain that an allergy is present is to give the patient the food in question under carefully controlled conditions. This is known as an allergy challenge.

The challenge test is usually offered for one of two reasons:

1. This test may be used after skin prick and blood tests have suggested a food allergy but the results are inconclusive.
             
2. This test may be offered when it is suspected that a person (often a child) has grown out of a particular food allergy, as is often the case with childhood allergies. 

Challenge tests are always undertaken in hospital under close medical supervision where resuscitation equipment and emergency medication are available in case a severe reaction occurs. This is a precaution, but one that is taken very seriously by staff involved.

To check for a reaction, small amounts of the allergen are given to the patient at set times. Sometimes, a small amount is first placed on the lips (this is called a lip dose). If no reaction is seen some of the allergen-containing food is then eaten. Care is taken over the amount of allergen eaten, and the timings, so that any reactions can be monitored carefully.

Sometimes the food is disguised in a ‘double-blind’ trial so that neither the tester nor the patient knows whether it is the allergen or a placebo (a harmless substance) which is being eaten. In this way, reactions caused by the idea of eating a risky food, can be avoided. 

If at any time there is a reaction, the challenge will be discontinued and appropriate avoidance advice will be given.

Important

The challenge test should ONLY be performed at hospital, with supervision by qualified medical staff and access to the necessary medical equipment