Food challenges

author 1, author 2 January 01, 2025 #tests #foods

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Prior to challenge risks/benefits discussed
Patient does not have any concurrent illness, does not use betablockers/ACEi or NSAIDs, has not recently had alcohol, has not exercised strenuously <2h prior to this visit, and is not sleep deprived.

Examination:
Vitals, skin exam, mouth exam

Procedure:
A total serving size of *** was used, which is about *** grams of food protein. It was done in *** steps, seperated by 30 minutes each. The patient was monitored about one hour after the last step.

Rationale:

Other in-vitro testing such as SPT or sIgE are not specific nor sensitive enough for true allergy. In addition, not all substances have validated tests otherwise (ie. most drug allergies). However, there is greater risk of anaphylaxis and death.

Reasons to perform include:

  • sIgE/SPT not consistent with history
  • chance of expanding diet; how important is that food to the patient
  • pre-test is low/moderate
  • assessing tolerance to cross reactive foods
  • assessing effect of different food forms

Safety prior to procedure

Did the patient do strenuous physical activities within 2 hours prior to challenge? Does the patient have an infection (eg. URTI) currently? Is the patient sleep deprived (<6 hours sleep)? Did the patient use any of these drugs in past 24 hrs (check all that apply)? No NSAIDs, beta-blockers, ACEis, H2-blockers, or PPIs. Do they have poorly controlled asthma, AD, or AR? Do they have unstable cardiac disease?

PROTOCOL

Examination and vitals prior

  • baseline good examination esp of oropharynex and skin, and lungs

Food form:

In most circumstances, it is preferable to challenge with the least processed or cooked form of the allergenic food that will be incorporated into the patient’s diet because tolerance of the most allergenic form of the food would provide a definitive answer, allowing the food to be introduced into the diet normally without restrictions An exception to this practice includes challenging with a BM or BE item because most milk- and egg-allergic patients may tolerate the baked form while reacting to the lesser-cooked form.44 In addition, it is not always practical to challenge to the most allergenic form of the food (eg, raw egg, raw fish, and undercooked beans).

proecedure

Variety of different approaches that are done. Some follow strict food protein/drug amounts and do 7 steps; others are much more practical. Below are approaches you've seen used before:

  1. PRACTALL protocol; 7 step, 15-20min inbetween
  2. Cumulative dose = age appropriate serving size, broken into 4-6 steps (usually exponential 'halfing' is fine). Sometimes do SPT beforehand to help stratify (unclear evidence for this). 20-30 mins inbetween.

Regardless:

if reactions, dubious, slow things down, ask

  • at every step, can ask if they want to proceed
  • hard to separate the pyschosomatic from true allergy
  • frequen reassessments to look for ana

AFter challenge

After a negative OFC (ie, the patient tolerated the food) the patient should be advised to avoid the food for the remainder of the day in case a rare delayed reaction to the food occurs. Patients are typically observed for at least 1 to 2 hours for an immediatetype reaction => avoid exercise

With a negative OFC, this Work Group recommends encouraging the patient to ingest the food in a manner typical of dietary consumption, at least eating it periodically

rough

peanut challenge syringe is pretty easy (doesn't work for all butters --- speaking from experience. Wear gloves if you are allergic -- also from experience) 0.4 ml 1 4 10 => 15 = 3tbsp

ask families to bring vehicles for food