Q:

3/29/2018
I have a question about a 6 year-old male who has a history of eczema that has not improved from infancy. I am considering doing an egg challenge. At 10 months old he had 3 episodes of facial, arm and abdomen hives within an hour of eating a whole egg. No other symptoms. His pediatrician did blood work and his serum IgE to egg white was 1.11 ku/l and egg yolk of 0.36. I saw him and did a skin test with results of egg white wheal and flare of 6mm/15 mm flare. The patient was already tolerating well baked egg and I advised he continue this but avoid 'unbaked" egg. He has done this and done well.

In 2016, at age 5 years old and visited for a re-evaluation. His IgE to egg white was 0.59 and egg yolk of 0. Unfortunately lab did not do component test. I skin tested him and it was negative to egg white and egg yolk. Mom did not want to pursue egg challenge at that time.

Now the patient has returned and his skin test to egg white and egg yolk remain negative. I ordered immunocap and component testing: Egg white: 0.54 ku/l, egg yolk 0.12 ku/l and component testing: of: ovomucoid less than 0.10 ku/l and ovalbumin: 0.48 ku/l (total IgE now 523-but skin without much eczema, no asthma or significant allergic rhinitis clinically). My question is really based on egg component testing presence of IgE to ovalbumin. Since heat labile is present in this child, would it suggest he might react to unbaked egg? I thought however that the component test may not suggest that as opposed to his overall IgE to egg white (which is now 0.54 ku/l). It is interesting that his total IgE now elevated to 523. Does unbaked egg challenge, i.e. French toast soaked in one egg, sound reasonable based on these results?

A:

We sought the expert opinion of Dr. Matthew Greenhawt. See his response below.

“Components will not help. I realize that there are “predictive” values for ovomucoid published, but they are flawed (for reasons that are too complex to go into). So, I would not be worried they were never sent. It’s a tool we are still trying to find a use for. There has never been a truly validated predictive level at a population level—only those that explained what happened in the small sample that was published. Those can’t generalize to your patient. The pretest probability of someone being baked egg tolerant is 80%. That’s the number to focus on. Everything else—its sample specific to “predict” things that I don’t think represent reality outside of the study. With a pre-test probability of 80%, in EBM a diagnostic test isn’t going to help.

I would challenge to unbaked egg. If you are concerned about those numbers, don’t be—those are pretty favorable. There is minimal sensitization being detected to just one thing, and none to anything else. I think you are in a good spot to try this. There is not a good marker for when these kids are ready to try unbaked egg, but generally sIgE below 2 is a pretty good indicator of at least a 50% chance of passing (and I think you are still at 50% even at higher sIgE). I wish we had a nice, neat value that would tell us what the outcome would be with high precision. But we don’t. You may want to use a bit more egg in that challenge, or make it a single jumbo egg, to get the protein content closer to 4g."

Patricia McNally, MD, FAAAAI

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