In a study of more than 100 children on food elimination diets based on positive serum IgE immunoassay results, oral food challenges (OFCs) demonstrated that most of the foods were being unnecessarily eliminated from the diet.
OFCs were not performed in children with:
- a history of a life-threatening reaction
- a convincing history of a reaction within the previous 6 to 12 months
- an immunoassay test result (level) that exceeded 95% predictive value for milk, egg, peanut, or fish
- an associated large prick skin test (PST)
For egg, milk, peanut, and fish allergy, diagnostic levels of IgE, which could predict clinical reactivity in this population with greater than 95% certainty, are:
- egg, 6 kilounits of allergen-specific IgE per liter kU
- milk, 32 kU (or 15 in newer studies)
- peanut, 15 kU
- fish, 20 kU
It is important to note that in 10–25% of food allergy reactions, sIgE can be undetectable by blood test (http://buff.ly/1e7HAmY).
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).
89% of oral food challenges (OFCs) performed with foods being actively avoided at baseline were negative.
All reactions during the OFCs occurred within the 2-hour observation period. There were no documented cases of atopic dermatitis flares on the day after an OFC.
84-93% of the foods being avoided were returned to the diet after an OFC, indicating that the vast majority of foods that had been restricted could be tolerated.
Many of the children were unnecessarily on "overly restrictive" diets that excluded foods that they had never eaten or foods that they once tolerated based primarily on sIgE test results (ImmunoCAP).
The erroneous practice of ordering a large panel of serum IgE tests and eliminating a large number of foods without the expertise of an allergist to interpret these tests must be changed.
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).
Oral Food Challenges (click to enlarge the diagram).
Study Warns of Over-Reliance on Blood Tests for Food Allergy. Medscape and Reuters, J Pediatr. Published online October 29, 2010.
Levels of specific IgE that predict food allergy reaction
Outpatient open oral food challenges should be considered if the likelihood of success is greater than 50%
Milk allergy resolution calculator from CoFAR http://bit.ly/U6TkNS - Mobile version: http://bit.ly/U6TmFn