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Diagnostic thresholds for free light chains in multiple myeloma depend on the assay used

Leukemia volume 32, pages 1815–1818 (2018)Cite this article

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Free light chains (FLCs) are helpful markers for the diagnosis, prognosis, and follow-up of patients with monoclonal gammopathy [1,2,3,4,5]. Freelite κ and λ reagents (The Binding Site) were the first commercially available reagents to measure FLC in serum [6]. These reagents are based on polyclonal antibodies raised in sheep [6]. The clinical relevance of Freelite has been extensively demonstrated [1,2,3,4,5]. Since 2011, Siemens offers the N Latex test, which is based on monoclonal antibodies, for FLC measurement [7]. Monoclonal reagents have the advantage of high lot-to-lot consistency and reproducibility. A possible disadvantage is that epitopes can be missed [8]. N Latex FLC results differ in absolute values from Freelite results [7].

Given these differences it is not clear whether diagnostic and prognostic thresholds proposed for Freelite also hold for N Latex. For example, in AL amyloidosis a baseline difference between involved and uninvolved light chain (dFLC) of 180 mg/L by Freelite corresponded to 165 mg/L by N Latex for survival and response to therapy was predicted by >50% decrease in Freelite dFLC or >33% decrease in N Latex dFLC [9].

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Acknowledgements

We thank Siemens and The Binding site for providing the reagents and for performing the assays. We thank Oscar Berlanga and Stephen Harding (both from the Binding Site) and Carola Wagner (from Siemens) for helpful discussions.

Author contribution

XB and MV designed the study and wrote the paper. XB, MV, MR, and DD analyzed the data. MD, KF, and BS take care of the patients with multiple myeloma and revised the manuscript. KP discussed the data and critically reviewed the study and the manuscript.

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Author notes

  1. Martine Vercammen

    Present address: Department of Laboratory Medicine, AZ Sint-Jan, Brugge, Belgium

Authors and Affiliations

  1. Laboratory Medicine, Immunology, University Hospitals Leuven, Leuven, Belgium

    Xavier Bossuyt, Martin Reynders & Koen Poesen

  2. Department of Microbiology and Immunology, Experimental Laboratory Immunology, Catholic University of Leuven, Leuven, Belgium

    Xavier Bossuyt & Doreen Dillaerts

  3. Department of Hematology, University Hospitals Leuven, Leuven, Belgium

    Michel Delforge

  4. Department of Nephrology, University Hospitals Leuven, Leuven, Belgium

    Ben Sprangers

  5. Department of Hematology, University Hospital VUB, Brussels, Belgium

    Karel Fostier

  6. Department of Neurosciences, Laboratory for Molecular Neurobiomarker Research, KU Leuven, Leuven, Belgium

    Koen Poesen

  7. Laboratory of Hematology, Universitair Ziekenhuis Brussel VUB, Brussels, Belgium

    Martine Vercammen

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Correspondence to Xavier Bossuyt.

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Conflict of interest

MV, KP, and XB received travel fees from The Binding Site. BS received research support from The Binding Site. The remaining authors declare no conflict of interest.

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Bossuyt, X., Delforge, M., Reynders, M. et al. Diagnostic thresholds for free light chains in multiple myeloma depend on the assay used. Leukemia 32, 1815–1818 (2018). https://doi.org/10.1038/s41375-018-0041-0

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