Establishing IMMULITE® 2000 cut-off values for serum allergen-specific immunoglobulin and exploring their relationship to exhaled nitric oxide

AIM Paediatric cut-off values for serum allergen-specific IgE (sIgE) using the Siemens IMMULITE(®) 2000 system to diagnose allergic rhinoconjunctivitis have not been established. We aimed to determine cut-off levels for sIgE for 10 common inhalant allergens and to study the relationship between sIgE, total IgE and fractional exhaled nitric oxide (FENO ). METHODS We enrolled 243 schoolchildren, including 164 with allergic rhinoconjunctivitis. Parental interviews, skin prick tests, sIgE, total IgE, FENO measurements, spirometry and exercise tests were performed. RESULTS Cut-off values with the best combined sensitivity and specificity were above the detection limit of the assay for seven of the ten allergens (0.23-1.1 kU/L). The overall accuracy of the IMMULITE(®) in detecting allergic rhinoconjunctivitis was good. sIgE was superior to total IgE and FENO in predicting allergic rhinoconjunctivitis to timothy, birch, mugwort, cat, dog and house dust mite. FENO was elevated in children with allergic rhinoconjunctivitis, irrespective of asthma. CONCLUSION Cut-off values for sIgE were dependent on the allergic phenotype and were above the IMMULITE(®) detection limit for seven of ten inhalant allergens. Consequently, using the detection limit for sIgE as the decision point would result in over-diagnosing allergic rhinoconjunctivitis. When measuring elevated FENO in children, allergic rhinoconjunctivitis should be suspected.