Food-specific IgE (FSIgE) cutoffs associated with 50% likelihood of negative OFC include:
- below 2 kUa/L to milk, egg, or peanut
- below 5kUa/L to peanut without history of previous reaction
Such children are appropriate candidates for oral food challenge (OFC) to investigate resolution of food allergy.
Oral Food Challenges (click to enlarge the diagram).
444 OFCs were included in this study. The proportions of negative OFCs performed based on FSIgE cutoffs alone were:
- 58 % for milk
- 42% for egg
- 63% for peanut
These are not great success rates, in particular, 42% rate of a negative challenge for egg is not very encouraging.
Here are the independent factors associated with negative OFCs:
- lower FSIgE levels (all three foods)
- higher total IgE (milk)
- consumption of baked egg products (egg)
- non-Caucasian race (eggs and peanuts)
Combinations of these factors identified subgroups of children with proportions of negative OFCs of:
- 83% for milk
- 75% for egg
- 75% for peanut
Combinations of clinical and laboratory elements (FSIgE values) might identify more children who are likely to have negative OFCs compared with current recommendations using FSIgE values alone. It is important to note that in 10–25% of food allergy reactions, sIgE can be undetectable by blood test (http://buff.ly/1e7HAmY).
The practical implications of this study are uncertain. The best approach is to see a board-certified allergist who will help the family select the best diagnostic method based on the combination of:
- history and physical examination
- skin test and blood test
- safety of the oral challenge
- importance of food introduction
8 top allergens account for 90 percent of food allergies. Specific IgE levels (sIgE) that predict the likelihood of passing an oral food challenge are shown in the figure. (click to enlarge the image).
Comparison of diagnostic methods for peanut, egg, and milk allergy - skin prick test (SPT) vs. specific IgE (sIgE) (click to see the spreadsheet). Sensitivity of blood allergy testing is 25-30% lower than that of skin testing, based on comparative studies (CCJM 2011).
Clinical and laboratory factors associated with negative oral food challenges. Allergy and Asthma Proceedings, Volume 33, Number 6, November/December 2012 , pp. 467-473(7).
AllergyCases.org: Food Challenges for Diagnosis of Food Allergy