The diagnostic value of skin prick testing in children with food allergy.

The diagnostic accuracy of the skin prick test (SPT) in food allergy is controversial. We have developed diagnostic cut-off levels for SPT in children with allergy to cow milk, egg and peanut. Based on 555 open food challenges in 467 children (median age 3.0 yr) we defined food-specific SPT weal diameters that were '100% diagnostic' for allergy to cow milk (>or=8 mm), egg (>or=7 mm) and peanut (>or=8 mm). In children < 2 yr of age, the corresponding weal diameters were >or=6 mm, >or=5 mm and >or=4 mm, respectively. These SPT cut-off levels were prospectively validated in 90 consecutive children <or=2 yr with challenge-proven food allergy. In young infants under 6 months of age who have not previously been exposed to a particular food item, the SPT were often negative or below the diagnostic cut-off but reached the diagnostic cut-off at the time of challenge in the second year of life. We assessed the diagnostic agreement between food-specific immunoglobulin E (IgE) antibody levels and SPT in a cohort of 820 infants and children under 2 yr of age (median age 13.1 months) with suspected allergy to cow milk, egg or peanut. When applying published 95%-positive predictive CAP values, the diagnostic accuracy of SPT and IgE antibody levels was similar for cow milk, but SPT was more sensitive in diagnosing allergy to egg (p < 0.0001) and peanut (p < 0.0001). Further studies are required to define age-specific diagnostic IgE antibody and SPT cut-off levels use in infants under 2 yr of age with suspected food allergies.