Allergen Specific Immunoglobulin E in Children Under 6 Years Old With Total Immunoglobulin E Below 10 kU/L

Laboratory diagnosis of type I hypersensitivity reaction is based on the determination of serum concentrations of total immunoglobulin E (tIgE) and allergen specific IgE (sIgE) antibodies. Serum concentration of tIgE varies throughout the lifespan. 1 Physiologic changes are mainly noticeable in the first decade of life. In spite of defined reference intervals for tIgE, as many as 5% of healthy children might have serum tIgE concentrations above the age-specific reference range, whereas 10% of children with clinical signs of hypersensitivity might have serum tIgE concentrations within the age-specific reference range. 1 As the concentration of circulating IgE antibodies might not always correlate with local tissue IgE synthesis, screening of sensitized individuals based on serum tIgE concentrations may prove inadequately reliable in some cases. 2 An increased concentration of sIgE indicates sensitization to a particular allergen. In sensitized individuals, only 5% of total sIgE production is found in the circulation, indicating current immune activity, whereas the rest of the sIgE is bound to tissue mastocytes and mediates local bioactivity. 3