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Comparison of 2 Serum-Free Light-Chain Assays in CKD Patients
Ben Sprangers1,2, Kathleen Claes1,3, Pieter Evenepoel1,3
1Department of Microbiology and Immunology, Laboratory of Molecular Immunology (Rega Institute), KU Leuven, Leuven, Belgium.
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.
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