Food allergy testing – oral food challenges

When might I be offered an oral food challenge?

A clinical immunology/allergy specialist may do an oral food challenge (OFC) to test whether:

• a certain food is the cause of an allergic reaction when unsure
• a person still has their previously diagnosed food allergy
• a food can be tolerated (eaten without signs of an allergic reaction) if it is baked, even if it can’t be eaten raw or lightly cooked. This is often the case for egg and milk where an OFC may show that baked egg or milk can be tolerated, even if the person is allergic to raw (or lightly cooked) egg or milk
• a person with a positive skin prick or blood test to a food (that they have never eaten) has a true allergy to that food.

What does an oral food challenge involve?

An OFC involves being fed the allergen in small and increasing amounts over a few hours. This is generally done in a hospital setting so that medical help and resuscitation equipment is close by if needed.

The Australasian Society of Clinical Immunology and Allergy (ASCIA) has protocols to guide health professionals on how the oral food challenge should be done.

A negative or positive challenge

If a person reacts to the food during an oral food challenge, then the challenge result is said to be positive. This means that the person is allergic to that food and they should avoid eating it. They will be treated with medication and observed by medical staff for the required time before leaving the hospital.

This is the same terminology that is used for a skin prick test. If you react to an allergen during a skin prick test, the test is said to be positive.

If a person does not react to the food during the oral food challenge, the result is negative. This means the person is not allergic to that food and they will  be advised to keep eating that food on a regular basis.

Words are important

It used to be said that someone had ‘passed’ a challenge if they did not have an allergic reaction and could safely eat the food after the challenge. If they had an allergic reaction and therefore could not eat the food, they were said to have ‘failed’ the challenge. The ‘pass or fail’ language is unhelpful for people with allergies as they may feel they have failed because of something they have or have not done.

Health professionals will now say a food challenge is either positive or negative or they will say someone ‘reacted to the food’ or ‘did not react to the food’.

Do I have to keep eating the food after a negative oral food challenge?

An OFC should not be done if the person with the allergy or their parent/carer do not plan to keep the food regularly in the diet following a negative challenge. Keeping the food in the diet is important. If the food is not eaten regularly, the food allergy is more likely to return.

How long will I have to be at the hospital for the challenge?

Most OFCs will take 2 hours as the food has to be eaten in increasing amounts and then there is usually 1–2 hours of supervision once the amount of food has been eaten. If anaphylaxis occurs, the person will be observed for the recommended 4 hours after the dose of adrenaline is given.

Useful links

ASCIA has further information on Food Allergen Challenges.