Interference of Xolair (anti-human IgE) in serological assays for total and allergen specific IgE

Abstract

Rationale The effect of Xolair (Omalizumab: monoclonal anti-human IgE) administration on the accuracy of serological immunoassays for IgE has not been reported. We studied the potential interference of Xolair on a widely-used, FDA-cleared immunoassay for total and allergen-specific IgE. Methods Sera from atopic adults [total serum IgE levels: 78-1186 kIU/L] were incubated (1hr,37oC; 16-18hrs,23oC) with constant volumes of buffer or 7-ten-fold concentrations of Xolair to obtain 8 anti-human IgE:human IgE molar ratios: 0-(sham control), 0.01, 0.1, 1, 10, 100, 1000, 10,000. Specimens were analyzed in duplicate in the Pharmacia FEIA CAP System for total and allergen-specific IgE antibody to 8 allergen specificities: yellow jacket venom, common ragweed, cat dander, dog dander, D. farinae, D. pteronyssinus, Alternaria alternata and Peanut. Results Minimal but reproducible artifactual decreases in measured total serum IgE up to 14% were observed when sera were incubated with 1 to 10 fold molar excess of anti-IgE to IgE. Greater interference was observed with all sera analyzed in the allergen-specific IgE assay. Allergen-specific IgE antibody levels in sham-control sera receiving no Xolair ranged from 0.82 to 65.70 kIU/L. Xolair interference was independent of allergen specificity but dependent on the initial level of allergen-specific IgE. Measured decreases in allergen-specific IgE from 10% to 54% were seen at therapeutically achieved anti-IgE:IgE molar ratios of 1 to 10. Conclusions Total serum IgE CAP analyses appear minimally altered by Xolair in serum, but allergen-specific IgE measurements on sera from allergic patients receiving Xolair should be interpreted with caution, since their accuracy may be compromised by anti-IgE interference.