Thank you for your inquiry.
Before answering your question specifically, a few comments are indicated.
First, the decision to do a challenge cannot be decided by anyone other than the physician caring for the patient and the patient themselves. The decision is in great part patient driven. It is made after a discussion of the risk/benefit ratio related to challenge. Tests are employed to allow a better evaluation of risk. Of course, the perceived risk will be different according to the physician's own experience doing challenges, and the perceived benefit is highly variable amongst patients.
So, the best that we can do is simply cite the data which deals with the likelihood of a reaction to challenge, and give a personal opinion in this regard.
The other comment is, I would do a skin test your patient. As you are aware, the skin test data are predictive of reactions. In this instance, the fact that your patient is on omalizumab does not rule out the performance of the skin test. It simply means that you could not trust a negative skin test. But if your skin test was 8 mm or more (varying studies have used a cutoff of 5 to 13 mm erythema), it would be of equal to or greater significance than if she was not on omalizumab. So, a negative test (or one less than 8 mm) would not be helpful, but a positive test should be as helpful to you as in vitro tests in making your decision.
Finally, no test has perfect predictability. There are occasional studies which have shown that in vitro tests do not correlate with the likelihood of challenge, and the cutoff points of predictability for negative and positive challenge have varied between studies. The only true test of sensitivity is the challenge itself.
Having made these comments, I will now try to answer your specific questions.
With the in vitro values that you do have, it is highly likely that your patient would react to an oral challenge to egg, and not unlikely that she would react to an oral challenge to baked egg. But in-office food challenges have been very safe, and physicians who perform them regularly frequently feel that a challenge to baked egg, even though a reaction is not unlikely, is indicated if the patient had a strong desire to free themselves of the fear of ingesting hidden egg allergens. In this child, who may be close to leaving home for college, such knowledge would be quite comforting, and may significantly improve her quality of life. So, if one feels comfortable in treating reactions in their office, a baked egg challenge would not be totally unreasonable in this instance. But an egg challenge (scrambled egg, et cetera) is so likely to produce a reaction in your case that it is doubtful many allergists would consider this indicated.
In direct answer to your question, even if you did a baked egg challenge and it was negative, I would not at this time proceed with a direct egg challenge. I think bringing your patient back in a year or two to reassess the sensitivity by repetition of the in vitro tests would be reasonable before considering a direct egg challenge.
Various articles have found that testing to certain allergens such as ovomucoid might be more accurate than to egg white, but data differ between investigations, and the same is true for ovalbumin. I personally feel that you could get all the information you needed by testing to egg white, with the possible addition of testing to ovomucoid.
In summary, I would do the following:
1. Skin test to commercially available egg . Although the cutoff points in terms of millimeters of erythema have varied, in general, 8 mm or above, especially since she is on omalizumab, would be highly predictive of a positive oral challenge to egg.
2. At this time, I personally would not consider a direct egg challenge, and I do not believe there is any consensus on whether or not you might do a baked egg challenge. But in my conversations with allergists who are experienced in doing this, after discussing the risk/benefit ratio with the patient, many would proceed if the patient was desirous of doing so.
3. I believe that using a skin test, and in vitro test to egg white and ovomucoid, you would have all the information you needed.
Thank you again for your inquiry and we hope this response is helpful to you.
1. Sampson and Ho. J Allergy Clin Immunol 1997; 100:444-51
2. Verstege A, et al. Clin Exp Allergy 2005; 35:1220-6.
3. Sporik R, et al. Clin Exp Allergy 2000; 30:1540-6.
4. Dieguez MC, et al Pediatr Allergy Immunol 2008; 19:319-24
5. Ando H, et al. J Allergy Clin Immunol 2008; 122(3):583-588.
6. Lemon-Mule, et al. J Allergy Clin Immunol 2008; 122(5):977-983.
7. Lieberman Jay, et al. J Allergy Clin Immunol 2012; 129(6):1682-1684.
8. Bartnikas L, et al. J Allergy Clin Immunol 2012; 131(2) (Supplement):AB82 (abstract).
9. Cortot CF, et al. Allergy Asthma Proceedings 2012 (May-June); 33(3):275-281.
10. Bartnikas L, et al. Annals of Allergy, Asthma, and Immunology 2012; 109(5):309-313.
11. Peters RL, et al. Pediatr Allergy Immunol 2012; 23(4):347-352.
12. Calvani M, et al. Pediatr Allergy Immunol 2012; 23(4):756-761.
Phil Lieberman, M.D.