Comparison of 2 Serum-Free Light-Chain Assays in CKD Patients

• Main Authors: Ben Sprangers, Kathleen Claes, Pieter Evenepoel, Dirk Kuypers, Koen Poesen, Michel Delforge, Xavier Bossuyt V, Björn Meijers
• Format: Article
• Language: English
• Published: Elsevier 2020-05-01
• Series: Kidney International Reports
• Online Access: http://www.sciencedirect.com/science/article/pii/S2468024920300401

Introduction: Quantification of serum-free light chains (FLCs) is important in the diagnosis and monitoring of paraprotein-related diseases. There are currently 2 FLC assays available: the Freelite assay (Binding Site) and the N Latex assay (Siemens). There is emerging evidence that these assays give different results, but it is not established how kidney dysfunction affects these assays differently. Methods: In this study, we measured and compared serum FLCs in patients with mild-to-moderate chronic kidney disease (CKD) using both assays. Results: Although κ FLCs are higher by Freelite, λ FLCs are higher by N Latex. Both κ and λ FLCs correlate inversely with estimated glomerular filtration rate (eGFR) in the 2 assays, but this effect is more pronounced in λ-free light-chain measurement by N Latex. Consequently, although the κ/λ ratio by Freelite is inversely correlated by eGFR, the κ/λ ratio by N Latex is positively correlated with eGFR. Conclusion: Our results clearly demonstrate that the 2 available FLC assays cannot be used interchangeably in patients with CKD. Keywords: assay, chronic kidney disease, free light chain