The atopy patch test in the diagnostic workup of suspected food-related symptoms in children.

BACKGROUND: There is an increasing need to develop test instruments that make oral food challenges superfluous. OBJECTIVE: We sought to study the utility of atopy patch tests (APTs) in the diagnostic workup of food allergy. METHODS: We investigated 437 children (median age, 13 months; 90% with atopic dermatitis) referred for evaluation of suspected food allergy. Specific serum IgE (sIgE) measurements, skin prick tests (SPTs), APTs, and controlled oral food challenges were performed. RESULTS: We analyzed 873 oral challenges with cow's milk, hen's egg, wheat, and/or soy. One thousand seven hundred single APTs were performed. As a single parameter, the APTs showed the best specificity compared with sIgE measurements, SPTs, or both. Combining the APT with either the SPT or sIgE measurement resulted in improved sensitivity and specificity. Decision points for sIgE measurement and for the SPT showed lower values when combined with a positive APT result. Correctly bypassing an oral food challenge with combined testing, including APTs, only between 0.5% and 7% (99% predicted probability) and between 6% and 14% (using 95% predicted probability) of children would fulfill the criteria for avoiding an oral food challenge. CONCLUSION: Although the predictive capacity of the APT is improved when combined with sIgE measurement or the SPT, oral food challenges become superfluous in only 0.5% to 14% of study patients. In addition, the APT is time consuming and demands a highly experienced test evaluator. CLINICAL IMPLICATIONS: For daily clinical practice, the APT adds only a small predictive value to the standard SPT and sIgE measurement in the diagnostic workup of suspected food-related symptoms in our study population.

Proposal for a standardized interpretation of the atopy patch test in children with atopic dermatitis and suspected food allergy.

The interpretation of the atopy patch test (APT) to foods is not standardized. This study aimed to validate the reading of the APT in terms of the diagnostic accuracy of individual skin signs. Eighty-seven children (mean age 2.4 +/- 2.5 yr, range 0.5-13.5; 57 male) with atopic dermatitis (AD) and suspected food allergies underwent APT to cow's milk, hen's egg, wheat and soy. Twelve-millimetre Finn chambers were applied for 48 h, and results were read after 48 and 72 h. Skin changes were graded for erythema, induration, papule formation and 'crescendo' phenomenon (increase of skin sign severity from 48 to 72 h). Food allergy was assessed by double blind, placebo-controlled food challenges (DBPCFC). Sensitivity, specificity and predictive values were calculated for each skin signs in relation to challenge outcome. Of 165 DBPCFC children, 75 (45%) were positive. The combination of any skin induration plus papules (seven or more), or of moderate erythema plus any induration plus seven or more papules had a positive predictive value (PPV) and specificity for the challenge outcome of 100%; however, the sensitivity was low (8% and 15%). The best diagnostic accuracy for single signs was found for induration beyond the Finn chamber margin (PPV 88%, specificity 99%, sensitivity 9%) and presence of at least seven papules (PPV 80%, specificity 96% sensitivity 21%). Presence of both induration and of at least seven papules at 72 h were the APT skin signs with the greatest diagnostic accuracy for food allergy in children with AD.