Establishment of age-dependent reference values for IgA subclasses.

Background: Recently, subclass-specific antisera have been introduced for application in a nephelometric assay. The aim of this study was to establish age-dependent reference values for serum concentrations of the two IgA subclasses in children and adults. Methods: Serum levels of IgA1 and IgA2 were measured by automated immunonephelometry in samples from 235 clinically healthy children between 6 months and 18 years of age and 36 healthy adults. Results: Both IgA1 and IgA2 were detectable in all samples, and both IgA1 and IgA2 increased with increasing age. In adults, the mean value for IgA1 is 1.46 g/l for IgA2 0.21 g/l and for total IgA 1.94 g/l. Individual IgA2 values correlate significantly (p<0.0001) with IgA1 values (r2=0.5433). In addition, there was a highly significant (p<0.0001) correlation (r2=0.9530) between the measured total IgA and the sum of the two IgA subclasses indicating that immunonephelometry using highly specific polyclonal antisera might be superior to other methods. Conclusions: These results and the availability of age-dependent reference values make it worthwhile to reassess the role of IgA subclasses in immunodeficiency and autoimmune diseases where conventional methods have led to conflicting results.