A new free light chain immunoassay shows advantages in the classification and in the follow-up of patients with paraproteinemia compared to a nephelometric assay

Background: For screening for monoclonal gammopathies, their prognostic stratification and therapy monitoring, the quantitative determination of free immunoglobulin light chains is a significant component.Nephelometric and turbidimetric test methods have so far been associated with analytical limitations and pitfalls.The new quantitative s-FLC ELISA (Sebia) was tested for its suitability for use in routine clinical diagnostics in an application study in a supraregional laboratory center in Germany.Materials and Methods: 510 samples in which the free light chains had previously been determined with the Freelite assays (The Binding Site) were compared with the new ELISA.Furthermore, the M-protein peak concentrations from 25 serum protein electrophoresis (SPE) were compared with the results of free light chain measurements of Freelite and Sebia FLC.Results: Only moderate correlations for the κ and λ light chains between the two methods, Sebia FLC ELISA and Freelite, were found.The concordance correlation coefficients (CCC) were only r=0.68 and r=0.67, respectively.There were significant quantitative differences between the two methods, which were particularly pronounced in samples with high FLC concentrations.The agreement between the immune fixation, which is considered the gold standard, and the Sebila FLC determination was 92.6%, but only 83.0% for the Freelite tests.The Sebia monoclonal FLC concentrations were consistent with the M protein concentrations determined with the SPE.Compared to this, the Freelite monoclonal FLC concentrations were consistently higher.The average overestimation was 10-fold compared to the SPE. Conclusion:The Sebia FLC Assay proved to be a robust platform for the sensitive and accurate determination of free light chains in serum.Due to the good agreement with the SPE and the conformity to the immunofixation as well as the low rerun rate resulting from the larger measuring range of the Sebia sFLC ELISA, these assays are suitable alternatives for the determination of free light chains for screening on monoclonal gammopathies as well as for the follow-up of patients with multiple myeloma.