Natural rubber latex-specific IgE antibodies in non-healthcare workers: comparison of two FDA-cleared in vitro kits

Latex-specific IgE antibody immunoassays are heavily relied upon in the diagnosis of latex allergy in the United States. The goal of this study is to compare anti-latex IgE levels measured by two U.S. Food and Drug Administration (FDA)-cleared kits (CAP® System and AlaSTAT® Microplate) in sera obtained from employees in non-healthcare industries. Sera were obtained from 381 workers employed in several, non-healthcare industries over the past 10 years, and stored frozen. All 381 coded sera were analysed for latex-specific IgE using the Diagnostic Products Corporation microplate AlaSTAT® and the Pharmacia-UpJohn CAP® System. Concordance between methods and intra- and inter-assay reproducibility were evaluated. Twenty-six sera gave positive results using the AlaSTAT® assay (26/381, 6.82%), while 24 yielded CAP® positive results (6.30%). There were no significant differences (p = NS) between the assays' measurements of latex-specific IgE antibody levels for all 381 sera, yielding 0.28 ± 0.19 kU L⁻¹ and 0.34 ± 0.59 kU_A L⁻¹, respectively. AlaSTAT® and CAP® assays agreed on the positive status of 9 (9/381, 2.4%) sera, and the negative status of 340 sera (340/381, 89.2%). The assays yielded discordant results on some individual sera. CAP® discordant results occurred in 17/26 sera (65.4%) of AlaSTAT® positive sera, while AlaSTAT® discordant results were found in 15/24 (57.7%) of the CAP® positive sera. The CAP® System, for instance, detected 0.39–2.3 kU_A l⁻¹ (1.03 ± 0.59, [mean ± SD]) of latex-specific IgE in the serum from 15 individuals that were all AlaSTAT® negative. In contrast, the AlaSTAT® detected 0.36–1.6 kU l⁻¹ (0.62 ± 0.31, [mean ± SD]) of IgE anti-latex in the serum from 17 subjects that were all CAP® negative. These data indicate that the a priori seroprevalence of latex-specific sera IgE is about 6%–7% in non-healthcare workers and that the CAP® and AlaSTAT® assays agree on the positive or negative status of the majority of sera (91.6%). However, caution should be exercised when applying FDA-cleared in vitro assays for latex-specific sera IgE in populations known to have potentially low concentrations of latex-specific IgE antibodies, as there appears to be a finite possibility for these assays to misclassify sera as being positive or negative for latex-specific IgE antibodies. Published in 1999 by John Wiley & Sons, Ltd.