Diagnosing peanut allergy with skin prick and specific IgE testing

Background: Food allergy is common in childhood. It has been suggested that the magnitude of a skin prick test or specific IgE result can improve diagnostic usefulness, but this has been addressed in only a few tertiary challenge-based studies. Objective: To determine the predictive value of a wheal >= 8 mm or serum specific IgE >= 15 kU(A)/L for clinical allergy and investigate whether results are generalizable. Methods: All subjects, up to 16 years of age, who had been investigated with a peanut or tree nut food challenge were eligible for the study. Subjects were referred from either a tertiary allergy clinic or a community birth cohort. All subjects with a history suggestive of food allergy were offered a challenge unless there were features of anaphylaxis. Details of challenges were prospectively recorded. Results were modeled by using logistic regression. Results: There was a total of 161 peanut challenges. Recent skin prick (longest wheal diameter) and specific IgE data were available for 135 and 136 challenges, respectively. The results suggest that a skin prick result >= 8 mm and a specific IgE >= 15 kU(A)/L have predictive values of 95% (95% CI, 76.2% to 99.9%) and 92.0% (74.0% to 99.0%), respectively, for a positive challenge. Age, the type of nut, and referral pattern of the subject did not appear to alter this relationship. Conclusion: These data suggest that a skin prick result >= 8 mm or a specific IgE >= 15 kU(A)/L have a high predictive value for clinical allergy to peanut and that these cutoff figures appear generalizable to different populations of children undergoing an assessment for peanut allergy.