IgG subclasses quantitation: Analytical performance of The Binding Site SPA® human assay and comparison with Siemens BNII® assay.

OBJECTIVES

Accurate evaluation of analyzers is highly recommended before these devices are broadly introduced for routine testing. Concerning quantification of IgG subclasses (IgGSc), standardization has not yet been reached and thus different assays might lead to different results. Here we report the analytical performances of The Binding Site (TBS) SPA® human IgGSc assay and the concordance with the Siemens BNII® human IgGSc assay.

DESIGN AND METHODS

We evaluated precision, LoB, LoD and linearity of TBS SPA® human IgGSc immunoassay. Quantitation of IgGSc in 53 patients' serum samples was performed in parallel on both analyzers. Results from both assays were compared.

RESULTS

Analytical performances of the TBS SPA® human IgGSc assay are acceptable for routine clinical use. According to the method comparison study, TBS assay measures lower values than Siemens assay for IgG1 and IgG4, whereas for IgG2 and IgG3 TBS provides greater values. All assays present a proportional bias, greater in the case of IgG3 and IgG4 assays. Individual subclass agreement, based on the classification of samples within three categories (low, normal and high) according to assay-specific reference intervals, range from 75% (IgG1) to 92% (IgG2). However, total classification agreement over all four subclasses only account for 55% of samples.

CONCLUSION

Results obtained from both assays are not interchangeable. Standardization of IgGSc assay and review of the reference ranges must be accomplished in order to achieve a higher degree of agreement between different methods.