Clinical implication by differential analytical performances of serum free light chain quantitation analysis using fully automated analyzers

Abstract Objectives Free light chain (FLC) is used for the diagnosis and prediction with regard to the progression risk of plasma cell disorders and Freelite reagent using the SPAplus analyzer (The Binding Site) has been one of the widely used option. However, N Latex FLC reagent with the Atellica CH 930 analyzer (Siemens Healthineers) has shown the advantages of automation and high throughput. We aimed to evaluated clinical implication by differential analytical performances of two assays. Methods A total of 322 serum samples were collected from 193 patients requested for FLC analysis including 131 multiple myeloma patients. The precision, linearity, dilution recovery of N Latex FLC assay was evaluated. We compared the two assays and analyzed the monomer-dimer pattern for discrepant results. Results The precision, linearity, and dilution recovery performance was appropriate for the routine use in clinical laboratories. Despite the good correlation within normal range, proportional bias up-to 170% was observed in samples with high concentrations especially for lambda. The higher value samples with N Latex FLC assay contained more monomer forms than controls. All opposite changes of FLC burden by the N Latex FLC assay proved to present concordant dynamic changes when assessed by serum protein electrophoresis. Conclusions Clinical laboratories should be aware of the inter-assay variability of FLC quantitative measurements using different platforms, especially for high concentrations of both kappa and lambda measurements, possibly due to monomer/dimer ratio diversity. Clinical interpretations for multiple myeloma disease status might not be dramatically affected only when the same assay is utilized during follow-up periods.