Fractional exhaled nitric oxide in infants during cow's milk food challenge

Cow's milk allergy (CMA) is the most common food allergy in early childhood. The golden standard for the diagnosis of CMA is a food challenge after a period of elimination. Increased levels of fractional exhaled nitric oxide (FE(NO)) have been shown after bronchial allergen provocation. We evaluated whether FE(NO) may also be a predictor of a positive reaction during cow's milk challenge in infants. Forty-four infants [mean age (range): 4.2 (3.7-4.6) months] suspected of CMA underwent an open food challenge with cow's milk formula administered in ascending quantities, starting with 2 ml and then 6, 20, 60 and 200 ml until a clinical reaction occurred. Off-line FE(NO) samples were obtained during tidal breathing by means of a facemask covering infants' nose and mouth. FE(NO) was measured twice before the challenge (baseline), immediately before each new dose of milk and after a positive reaction or after the last dose of milk. Eleven children showed immediate positive clinical responses to cow's milk, whereas 13 infants presented only a late-type reaction. FE(NO) values before or after a positive reaction (either immediate or late) were not different from FE(NO) values at baseline. Baseline FE(NO) in infants with a positive reaction did not differ from FE(NO) in infants without a reaction at any time point. We conclude that FE(NO) values are not predictive and not related to the occurrence of a positive reaction during a cow's milk challenge in infants, suggesting that a positive reaction may not result from eosinophilic activation.