The vast majority of subjects with a negative fresh food SPT of the EH food product had successful OFCs to the baked muffins. Fifty-five of the 58 patients tolerated the oral challenge and were encouraged to re-introduce baked eggs or milk into their diets, whereas three reacted and were assumed to be allergic to the food products in all forms. Only one of the three had an anaphylactic reaction (Figure 3). The negative predictive value for the SPT with the extensively heated food product was 94.8%.
This study is the first to propose performing a fresh food SPT in children with milk and egg food allergies in order to predict outcomes of an OFC with EH food. This may serve as a practical marker for children likely to be tolerant of EH milk and egg OFCs. Although previous studies have shown that the majority of food-allergic children tolerate the same foods in their EH forms, the proportion of children experiencing an allergic reaction during the OFC remained significant. Reaction rates of 23% were reported by two separate studies, one challenging milk-allergic children to an OFC with EH milk and the second challenging egg-allergic children to an OFC with EH egg products. Twenty-three out of a sample size of 100 reacted in the milk allergy study, whereas 27 out of 117 reacted in the egg allergy study [3, 4]. In our study, the risk of reaction during the diagnostic process was reduced from 23% to 5% by performing an SPT with EH foods prior to their OFC.
Many studies have explored the utility of serologic testing in both the diagnosis of allergy as well as ability to predict tolerance to EH products. For example, specific IgE antibodies to the egg protein ovomucoid have been suggested to be predictors of reactivity to EH egg products, and clinical decision points have been proposed . A recent study suggests a role for the specific IgE/IgG4 antibodies to ovalbumin (OVA) and ovomucoid (OVM) in predicting reactivity to extensively heated egg products in egg-allergic children, however this is not a clinically practical or available option . Neither food-specific IgE levels nor SPT responses to commercial food extracts are entirely reliable in identifying children likely to be tolerant of EH milk and egg products . Our proposal to incorporate fresh food SPT in the diagnostic evaluation of milk and egg allergic children may serve as a practical, easy alternative in an allergist’s clinic.
Nevertheless, this study has some limitations. There are inherent flaws in any retrospective study, including lack of blinding of any party. While physician notes from patient encounters were detailed, the data were not originally collected for the purpose of research. Furthermore, the sample size was small, non-homogeneous for one food allergy, and had a much larger egg-allergic cohort. Baseline characteristics between milk and egg allergic individuals were not entirely balanced, and it is unclear whether this is due to a true difference between the two populations. Future studies should assess milk and egg food allergies separately. Although parents were given specific instructions with regards to how to bake the muffins, this factor was not otherwise controlled. Moreover, data were insufficient for calculations of positive predictive value, specificity and sensitivity. Lastly, this study was performed at one centre with the observations and clinical judgment of one clinician; larger multi-clinician, multi-centre trials would be able to better substantiate our findings.