What is the optimal occlusion time for the atopy patch test in the diagnosis of food allergies in children with atopic dermatitis?

The atopy patch test (APT) is a valuable additional tool in the diagnosis of food allergies in children with atopic dermatitis (AD). Nevertheless, this technique needs to be standardized, and this is particularly true for the occlusion time. We compared the results obtained after a 24-h occlusion period with those obtained after a 48-h occlusion period, the usual occlusion time used in contact allergy. We performed 64 open oral food challenges in 48 children (30 boys and 18 girls), aged between 3 and 29 months (median 14 months). The sensitivity, positive predictive value and negative predictive value were all better for the 48-h occlusion time than for the 24-h occlusion time. Therefore, the recommended occlusion time for the APT with foods should be 48 h, as for contact allergens.