PURPOSE OF THE STUDY.
The goal of this study was to investigate if a skin prick test to ovomucoid and baked egg could predict which patients would pass an oral food challenge (OFC) to baked egg.
This prospective study evaluated 143 children from the allergy clinics at the Children’s Hospital at Westmead (Sydney, Australia). These children had a high probability of egg allergy based on either: (1) clinical reactions to egg within the 12 months before the study and positive skin prick test result or serum-specific IgE to egg white; or (2) skin prick test result or serum-specific IgE to egg white >95 positive predictive values previously established in those who did not ingest egg.
Subjects underwent skin prick testing to egg white, ovomucoid, and baked egg muffin homogenized with normal saline on the day of the OFC. The skin prick tests were performed according to standard techniques, and positive results were wheal size at least 3 mm greater than that of the saline control subject at 15 minutes. The OFC used baked egg muffins with 1 g of egg per muffin challenge.
A total of 143 OFCs were conducted; 90 (63%) were negative. Of the 53 failed challenges, 3 had severe reactions. The medium skin prick size for failed challenges was 6.0 mm for muffin, 7.5 mm for ovomucoid, and 9.0 mm for egg white, whereas the size for passed challenges was 4.0 mm, 5.0 mm, and 8.0 mm for muffin, ovomucoid, and egg white, respectively. Skin test size did not predict severity. A skin prick test size of <2 mm to the baked egg muffin had 88% negative predictive value and a skin prick test size of ≥11 mm to ovomucoid had a positive predictive value of 100%.
The results of this study found that skin prick tests to ovomucoid and to baked egg muffin homogenized with normal saline could be helpful in deciding if egg-allergic patients are ready for OFC to baked egg. A skin prick test result of <2 mm to muffin had an 88% negative predictive value and an ovomucoid skin prick test result ≥11 mm had a positive predictive value of 100%.
Although it is known that 60% to 70% of egg-allergic children can tolerate “baked egg” in their diet, it is often difficult to identify this subpopulation. Recently, ovomucoid-specific IgE levels have been shown to be useful in helping predict the outcome of OFCs to baked egg, but only when the levels are >10 kUa/L (97% positive predictive value). This study uses 2 new skin testing reagents (ovomucoid and muffin suspension) in an attempt to identify who might be able to eat baked egg. Using this approach, a 100% positive predictive value and an 88% negative predictive value have been determined. Although the majority of egg-allergic children will fall outside of these parameters, this approach could reduce the need for OFCs. Importantly, the skin response did not predict the severity of the reaction.
- Copyright © 2014 by the American Academy of Pediatrics