D2.45 - Specific IgE for inhalant allergens: A cutoff of 0.35 kUA/L is too low

Measurement of specific immunoglobulin E (sIgE) is often used interchangeably with skin prick test (SPT) to detect allergic sensitization. Evidence of concordance between the two methods for aeroallergens in children is limited and the arbitrary sIgE cutoff value of 0.35kUA/L is used uniformly for all allergens.

The aim of the study was to evaluate the agreement between sIgE with cutoff 0.35 kUA/L and a positive SPT (cutoff 3 mm) for ten aeroallergens and to investigate the sIgE level that corresponds best with a positive SPT in school-aged children. 

Measurement of sIgE and SPT for birch, grass and mugwort pollen, horse, dog, cat, Dermatophagoides pteronyssinus, Dermatophagoides farinae, Alternaria and Cladosporium were performed in 300 children aged 6 to 14 years, 132 children with asthma and 168 controls. The agreement between sIgE and SPT for the individual aeroallergens was assessed by Cohen´s kappa coefficient with different sIgE cutoff values.

In total, the 300 children had 297 positive SPT and 445 positive IgE analyses. The incidence of sensitization to Alternaria and Cladosporium was too low for further analysis.

The agreement between sIgE cutoff 0.35 kUA/L and SPT cutoff 3 mm was moderate to substantial for the remaining 8 aeroallergens.  The estimated optimal sIgE cutoff level that predicted a SPT ≥ 3 mm was 0.75 kUA/L for grass, horse, dog and cat, 1.0 kUA/L for mugwort, 3.0 kUA/L for D. pteronyssinus and D. farinae and 5.0 kUA/L for birch. Using a sIgE cutoff of 0.75 kUA/L increased the agreement for all 8 allergens. 

Based on the premise that a SPT of at least 3mm is the gold standard for detecting sensitization, our data suggest that a cutoff of sIgE is too low. A cut off of 0.75 kUA/L correlated better with the SPT.