Delayed- and immediate-type reactions in the atopy patch test with food allergens in young children with atopic dermatitis

In recent years, the atopy patch test (APT) has been suggested as an addition in the allergological work-up of children with atopic dermatitis (AD) and suspected food allergy. We initiated a prospective clinical study in children with AD younger than 3 yr, to evaluate the additional clinical value of the APT next to our own standardized allergological work-up in case of a suspected food allergy. One hundred and thirty-five children were included in the study. They were tested using the skin application food test (SAFT), the APT and measurement of specific IgE. The allergens used in the skin tests were freshly prepared food stuffs and included commercially available cow's milk (CM), the egg white of a hard boiled hen's egg and mashed peanuts in a saline solution. Allergy was defined using a flowchart incorporating the results from the SAFT, oral challenges (OCs) and elimination and (re)introduction periods. To determine the additional value of the APT next to the SAFT, we analyzed the SAFT negative patients per allergen and used an exact binary logistic analysis to evaluate the simultaneous effects of the APT and measurement of specific IgE, calculating mutually adjusted odds ratios (ORs) for positive APTs and specific IgE levels above 0.70 U/l. We found clinically relevant food allergies in 23% (egg white) to 28% (CM and peanut) of our study population. Positive SAFT reactions were observed in 14% (peanut), 16% (egg white) and 21% (CM) of our patient population. Next to the SAFT, we did not observe a significant additional value of the APT for the diagnosis of CM or egg white allergy, but we did find a significant additional value for the diagnosis of peanut allergy (OR = 11.56; p < 0.005, 2-sided). In clinical practice this statistically significant value does not exclude the need for OC and controlled elimination and (re)introduction periods due to the presence of false-negative as well as false-positive results in the APT. In conclusion, we could not find enough support for the current addition of the APT to our standardized allergological work-up in young children below the age of 3 yr with AD and suspected food allergy. At the moment the additional value of the classical delayed-type APT next to the SAFT seems to be very limited at best in this study population and does not justify the time-consuming nature of the skin test.