Evaluation of the N-latex serum free light chain assay on the Siemens BNII analyzer and agreement with The Binding Site FreeLite assay on the SPA Plus

摘要

Abstract Objectives To evaluate the Siemens N-latex kappa free light chain (κFLC) and lambda FLC (λFLC) assays on the BNII nephelometer and assess agreement with The Binding Site Freelite FLC assays on the SPA Plus . Design and methods Over 180 patient serum samples from routine analysis of κFLC and λFLC measured by the Freelite assay were collected for the study and measured with the N-latex κFLC and λFLC assays to assess precision, linearity, method comparison and dilutional effects. Results Complex precision showed coefficients of variation of 4.8–7.2% for the κFLC assay and 3.6–6.0% for the λFLC assay. Linearity assessment showed both assays were linear (κFLC, y=1.00x?0.09 and λFLC, y=1.050x?1.252). Qualitative method comparison showed 87.9% (116/132) agreement and Cohen's kappa of 80.4% between the κFLC assays and 72.6% (98/135) agreement and Cohen's kappa of 55.4% for the λFLC assays. Quantitative method comparison for κFLC R =0.661 and for λFLC R =0.526. Dilutional effects including antigen excess and non-linearity were also examined. Conclusions The N-latex assay showed good precision and linearity with reasonable agreement to the Freelite assay. However, the assays should not be used interchangeably to monitor patients. Highlights ? The N-latex κFLC and λFLC assays show good precision and linearity. ? N-latex and Freelite assays demonstrated reasonable qualitative correlation. ? Variability in results between assays for both kappa and lambda was observed at very high FLC values. ? N-latex κFLC and λFLC assays may be less susceptible to dilutional effects than the Freelite assays. ? The assays should not be used interchangeably to monitor patients.