Methodologic problems in establishing normal values for IgG subclass concentrations in a pediatric population; comparison of radial immunodiffusion and ELISA methods.

The aim of this study was to establish an enzyme-linked immunosorbent assay (ELISA) to measure IgG subclasses by means of monoclonal antibodies. The distribution of IgG subclass protein concentrations in sera from 227 healthy Danish children and 90 adults was measured. Furthermore, this newly established ELISA was compared with different assay systems for determination of IgG subclasses: two radial immunodiffusion methods (RID), one using polyclonal and one using monoclonal antibodies, as well as a commercially available ELISA kit. There was good agreement of results obtained by the different methods of measuring IgG3 and IgG4 concentrations. There was good correlation between results obtained by both RID methods. Despite good correlation between the assays, the ELISA kit showed higher levels of IgG1 in all investigated sera, and the ELISA kit showed no correlation with the other methods, when IgG2 was measured. Analysis of the normal ranges measured by ELISA developed in our laboratory and by RID with polyclonal antibodies showed that the levels obtained by RID were higher than those obtained by our ELISA in sera with low levels of both IgG1 and IgG2, and lower in sera with high concentrations of these two immunoglobulins. Our results emphasize the importance of establishing age-related normal limits for any novel assay measuring IgG subclass concentrations.