Improved screening for peanut allergy by the combined use of skin prick tests and specific IgE assays.

BACKGROUND

The diagnosis of peanut allergy must be based on reliable, safe criteria. Double-blind, placebo-controlled food challenges (DBPCFCs) are the gold standard but are costly and dangerous because they can trigger severe reactions.

OBJECTIVE

The aim of this study was to develop a new strategy for diagnosing peanut allergy while reducing the need for DBPCFCs.

METHODS

We studied 363 children referred for an evaluation of suspected food hypersensitivity. They all benefited from the same diagnostic strategy, which included, in order, clinical history, a skin prick test (SPT), and a specific IgE assay. DBPCFCs were performed on all the children by personnel who were unaware of the results of the other tests. To assess the performance characteristics of the SPT (comparing commercial and raw peanut extracts) and the specific IgE assay, we compared the results with those provided by the DBPCFCs. For SPTs and specific IgE assays, we sought to determine the cutoff values required to exclude false-positive and false-negative results.

RESULTS

According to DBPCFC results, 177 children were allergic to peanut, and 186 were not. The performance characteristics of the SPTs were superior with the raw extract because the negative predictive value was 100% (95% confidence interval [CI], 97.5-100). If the skin reaction with the raw extract was less than 3 mm, we could be quite certain that the child was not allergic. On the other hand, if the SPT resulted in a wheal diameter of larger than 3 mm, we could only be 74% certain that the children were allergic. Furthermore, if the SPT resulted in a wheal diameter of 16 mm or larger, we could be quite certain that the child was allergic because the positive predictive value was 100% (95% CI, 86.8-100). Specific IgE concentrations of 57 kU(A)/L or greater were associated with a positive predictive value of 100% (95% CI, 87.2-100). The combined use of the tests resulting in a positive diagnosis if the SPT result was 16 mm or larger or specific IgE concentration was 57 kU(A)/L or greater and in a negative diagnosis if the SPT result was less than 3 mm and the specific IgE concentration was less than 57 kU(A)/L allowed us to classify subjects with almost complete certainty as being allergic or not because the predictive values were 100%.

CONCLUSION

Commercial extracts could not be used to reliably predict tolerance of peanut. Peanut DBPCFCs can be avoided when SPTs with raw extracts resulted in wheals with a largest diameter of less than 3 mm and a specific IgE concentration of less than 57 kU(A)/L and also when wheal diameters were 16 mm or larger or specific IgE values were 57 kU(A)/L or greater. Otherwise, DBPCFCs were indispensable for the unequivocal diagnosis of peanut allergy.