Food And Drug Reactions And Anaphylaxis
Improved screening for peanut allergy by the combined use of skin prick tests and specific IgE assays

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Abstract

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 kUA/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 kUA/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 kUA/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 kUA/L and also when wheal diameters were 16 mm or larger or specific IgE values were 57 kUA/L or greater. Otherwise, DBPCFCs were indispensable for the unequivocal diagnosis of peanut allergy. (J Allergy Clin Immunol 2002;109:1027-33.)

Section snippets

Study population

We conducted a cross-sectional study with 363 children referred for an evaluation of suspected food hypersensitivity. They had not been given a diagnosis of peanut allergy at the time of inclusion, but we systematically tested for this allergy because peanut is the most common food allergen in France. The children were all subjected to the same testing procedure, which was always performed in the same orderand at the same time: clinical history, SPT with commercial and fresh (raw) extracts,

Study population

Three hundred sixty-three children were included in the study. On the basis of the DBPCFC results, 177 children were allergic to peanut, and 186 were not. The median age was 4.0 years (range, 0.1-15.9 years), the boy/girl sex ratio was 1.8, and 67.5% (245/363) had a family history of atopic disease. All 186 children with a negative DBPCFC result had one or more allergies to foods other than peanut: allergies confirmed by DBPCFCs performed with the same procedure as the peanut oral food

Discussion

The DBPCFC is universally recognized as the gold standard for the diagnosis of peanut allergy because of its 100% sensitivity and specificity. Clinical histories, SPTs, and specific IgE assays can indicate a possible diagnosis of peanut allergy. Nevertheless, suggestive clinical histories are validated by DBPCFCs in less than 50% of subjects.26 The effect of a diagnosis of peanut allergy on an individual's lifestyle in terms of school or work performance, leisure activities, and financial burden

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  • Cited by (0)

    Reprint requests: Fabienne Rancé, MD, Allergologie, Hôpital des Enfants, CHU Toulouse, 330 avenue de Grande-Bretagne, 31026 Toulouse cedex, France.

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