N Latex FLC – new monoclonal high-performance assays for the determination of free light chain kappa and lambda

Henk te Velthuis, Ingrid Knop 1 , Peter Stam 1 , Monic van den Broek 1 , Hannie Klaasse Bos 2 , Suzanne Hol 1 , Elisa Teunissen 1 , Karin Schulte Fischedick 1 , Harald Althaus 3 , Brigitta Schmidt 3 , Carola Wagner 3 , and Roel Melsert 1
  • 1 Sanquin Reagents, Sanquin Blood Supply, Amsterdam, The Netherlands
  • 2 Department of Immunopathology, Sanquin Research and Landsteiner Laboratory, Academic Medical Center, Amsterdam, The Netherlands
  • 3 Department of Plasma Proteins, Siemens Healthcare Diagnostics, Marburg, Germany

Abstract

Background: High serum concentrations of monoclonal free light chain (FLC) kappa or lambda are markers of plasma cell dyscrasia.

Methods: We developed new, latex-enhanced, specific nephelometric assays based on monoclonal antibodies for the determination of FLC kappa and lambda in serum, EDTA plasma and Li-heparin plasma for use on the Siemens BN™ systems.

Results: Reference ranges were determined from 369 samples: FLC kappa 6.7–22.4 mg/L, FLC lambda 8.3–27.0 mg/L and kappa/lambda ratio 0.31–1.56. Protection from falsely low results due to antigen excess is obtained with a built-in pre-reaction in the assay protocols. Lot-to-lot consistency between three different lots of reagent, calibrators and supplementary reagent lots showed normalized differences <7.5%. The reproducibility of serum samples varied between 4% and 7%. The method comparison with Freelite™ assays showed normalized differences of 19.7%, 32.7% and 21.7%, respectively, for FLC kappa, lambda and ratio, correlations of 0.94, 0.77 and 0.73, and concordance rates of 99.2%, 94.2% and 95%.

Conclusions: N Latex FLC demonstrates high precision, good lot-to-lot consistency and freedom from a high-dose hook effect. The method comparison between Freelite™ and the N Latex FLC assays showed good clinical concordance. Further studies need to reveal the clinical value of the new FLC assays.

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