Gold standard for diagnosis of a food allergy or intolerance. A challenge is only considered complete once a normal age-appropriate portion of the food has been consumed.

In certain cases, food challenge is potentially more dangerous, and should only be done after assessment and discussion of likely risks and benefits. If there is no reaction (“negative challenge”) then of course there will be less fear and more food options [at least if food is consumed regularly]. If there is a reaction (“positive challenge” is the preferred term, not “failed”) then there is no longer any doubt, and the child/family will experience a reaction (useful if child does not remember) and see how it is managed. Lots of families say that using their adrenaline autoinjector for the first time (if it comes to that) takes away a lot of the anxiety about using it in future, which is very useful. So always check patient/family prepared to administer if required.

Objective measures of symptoms/signs preferred. Eczema, wheeze, congestion, diarrhoea should all have resolved (or be optimal) prior to doing the challenge, to avoid potential confusion. The challenge can be blinded if there is still doubt.

2024 PRACTALL update (Hugh Sampson)

Discussion about reliability of skin prick tests etc. Table of PPVs based on Riggioni metanalysis.

In terms of safety, severe reactions possible even with milligram level doses (and even in children with tolerance to baked versions!). Test results do not predict, other than possibly 2S albumins and tree allergy.

Outpatient clinic rooms are included in potential setting. Other considerations are delayed reactions; asthma; previous reactions to trace amounts; whether on elimination diet (?).

IV access should be considered if prior “severe anaphylaxis”, severe asthma, or likely difficulties getting access if required.

Lots of levels useful if trying to establish threshold, but makes it harder to achieve “typical” dose within time available – and potential for “rush desensitisation” effect! Some reports that multiple dosing can cause reactions where single dose wouldn’t… So some regimens combine logarithmic and semi-logarithmic increases.

Target dose generally 2-3g protein. 5% false negative rate for 875mg (cumulative 3500mg) top dose. Shellfish particularly needs a high target dose, fish similarly. But depends on size of child too…

Suggests 1 egg, 140-200ml milk, 28g cheese, 2g peanut, 3g tree nut.

Lip challenges not recommended as little data, all suggesting it is unhelpful.

Dosing intervals typically 15-20 mins but not very logical, given many reactions take longer eg milk, peanut, cooked egg. So now recommends 20-30 mins…

For FPIES, have IV fluids and ondansetron available. Check IgE/SPT negative! Consider methylprednisolone (but no data!). Taking baseline and 4-6hr neutrophil counts useful (>1500 cells/ml rise diagnostic where symptoms subjective). 0.06–0.3 g of food protein per kilogram body weight (maximum 3 g protein), administered as a single serving or as 2–3 servings every 15–30 min, followed by 4 h observation.

Else, 1/3 of the food portion for age is done under physician observation followed by a home titration to a full dose (very low rate of mild (mostly diarrhea) delayed reactions later during the day of the OFC or within the first few days of home dosing) – better than risk of causing severe symptoms during a single feeding with a higher dose of food. Some reports of FPIES recurrence after negative challenge…