Gal d 1-specific IgE predicts allergy to heated egg in Finnish children

BackgroundAllergen-specific IgE levels can be useful in predicting outcomes of oral food challenges, but optimal cutoff levels vary in different populations. The aim was to determine cutoff values for egg white- and Gal d 1-, Gal d 2-, Gal d 3-, and Gal d 4-specific IgE (sIgE) predicting positive oral heated egg challenges in 185 Finnish children and adolescents. MethodsA total of 185 egg-sensitized patients (age: 1-19years, median: 6.3, mean: 7.0years) with suspected egg allergy underwent double-blind, placebo-controlled (n=78), or open (n=107) oral food challenges with heated egg white. Specific IgE levels to egg white, Gal d 1 (ovomucoid), Gal d 2 (ovalbumin), Gal d 3 (conalbumin), and Gal d 4 (lysozyme) were measured by ImmunoCAP and compared with challenge outcomes. ResultsOf the 185 challenges, 124 (67%) were positive. Gal d 1 sIgE levels were significantly higher in the challenge-positive (median 13.5kU/L, mean 33.2kU/L) than in the challenge-negative group (median 0.2kU/L, mean 1.2kU/L), P<0.0001. The diagnostic capacity of sIgE to egg white and Gal d 2, 3, and 4 was clearly weaker. In ROC analysis, the AUC for egg white was 0.86, Gal d 2 0.84, Gal d 3 0.79, and Gal d 4 0.77. Sensitization to Gal d 1 with a cutoff of value of >3.7kU/L predicted a positive challenge with a specificity of 95% and sensitivity of 78%. The likelihood ratio was 15.9. In ROC analysis, the area under the curve was 0.94 (95% CI, 0.91-0.97). With a cutoff value of >14kU/L, all challenges were positive, and with a cutoff of <0.9kU/L, 95% of the challenges were negative. In the children aged 1-5years (n=88), the cutoff for Gal d 1 was >3.8kU/L, and in the children above 6years of age (n=97), it was >3.5kU/L. ConclusionGal d 1-specific IgE is useful in distinguishing egg-sensitized patients with clinically reactive egg allergy from those tolerant of heated egg. The optimal cutoff point in a Finnish population of 185 children and adolescents was 3.7kU/L with no significant difference between the younger and older age groups.