Evaluation of the siemens N Latex free light chain assay and comparison to Binding Site Freelite™ assay

Abstract

Abstract Introduction/Objective The International Myeloma Working Group (IMWG) guidelines include serum free light chain (sFLC) level and κ/λ ratio as excellent indicators of clonality. The Binding Site Freelite ™ was the first FDA approved assay for quantitative measurement of sFLC, the assay was based on a mixture of polyclonal antibodies directed against a variety of FLC epitopes. The Siemens N-Latex assay employs a probe mixture of mouse monoclonal antibodies. Both assays can be run on nephelometers. We assessed the analytical performance of the N-Latex assays and compared it with the Freelite™ assays. Methods/Case Report Analytical accuracy, precision, reproducibility and linearity were evaluated according to the regulatory standards. Method comparison was performed with 220 clinical samples for statistic correlation and clinical concordance analysis. Results (if a Case Study enter NA) The N-Latex FLC κ and λ assays had coefficient variation of 1-5% with-in run and 3-8% between run precision. Accuracy was verified using assayed controls in the duration of 21 days. Within analytical measuring range, almost perfect linearity was achieved for both κ and λ FLC assays. In comparison study to Freelite™ with 220 clinical samples, good agreement in classification was observed for κ, λ and κ/λ ratio (Cohen’s κ 0.73, 0.82 and 0.87). Pearson correlation analysis showed correlation coefficient value r >0.90 for all the analytes. Conclusion The N-Latex FLC assay has good analytical performance, did not exhibit gross antigen excess and can be used in clinical practice. However, it showed markedly lower absolute values for κ/λ ratio compared with Freelite™. Our data demonstrated that although good clinical concordance between N-Latex and Freelite™ FLC assays was achieved, the absolute values from the two assay are not interchangeable. Further studies in modification of the assay-specific diagnostic (involved FLC/non-involved FLC) thresholds for smoldering multiple myeloma (SMM) and multiple myeloma (MM) are needed.