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 SPAPlus

Publication date: Available online 13 May 2017
Source:Clinical Biochemistry
Author(s): Nicole M.A. White-Al Habeeb, Tammy Earle, Megan Spencer, Ivan M. Blasutig
ObjectivesTo 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 SPAPlus.Design and methodsOver 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.ResultsComplex 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<150mg/L was y=0.92x+2.21, R=0.661 and for λFLC<150mg/L was y=7.90x−137.96, R=0.526. Dilutional effects including antigen excess and non-linearity were also examined.ConclusionsThe 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.



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