Method comparison of three serum free light chain assays on the Roche Cobas 6000 c501 chemistry analyzer.

Dieuwertje Augustijn,Henk Russcher,Joannes F.M Jacobs

doi:10.1515/cclm-2021-1029

Abstract

Free light chains (FLC) are important in the diagnosis, prognosis and monitoring of therapy response of patients with monoclonal gammopathies. In this study, we performed a method comparison of three FLC assays onthe Cobas 6000 c501 chemistry analyzer of Roche Diagnostics. Samples of 119 patients with various monoclonal gammopathies and 26 control patients were measured with the Freelite (The Binding Site), Diazyme (Diazyme Laboratories) and KLoneus (Trimero Diagnostics) FLC assays. A method comparison was performed and reference intervals of the three assays were validated. The analysis of the Bland-Altman agreement showed bias between the three FLC assays, ranging from-62.7 to 5.1% for κFLC and between-29.2 to 80.5% for λFLC. The Freelite and Diazyme assays have the highest agreement. The concordance of the FLC-ratio ranges from 41 to 75%, with the highest concordance between the Freelite and KLoneus assays. The FLC-ratio in 25 sera from healthy controls were within the reference ranges of the Freelite and KLoneus assays. The FLC-ratio was elevated in all 25 samples tested with the Diazyme assay. The agreement for the free light chains is highest between the Freelite and the Diazyme assay and fair for the KLoneus assay. However, concordance of the FLC-ratio is highest when the Freelite and KLoneus assays were compared. Our data suggest that concordance for the Diazyme assay could be improved by recalibration. Because of absolute differences between the three methods in individual patients, none of the three FLC assays can be used interchangeably.

Highlights

Monoclonal gammopathies are characterized by clonal proliferation of plasma cells leading to the production of monoclonal immunoglobulins, the so-called M-proteins
We performed a method comparison of three Free light chains (FLC) assays on the Cobas 6000 c501 chemistry analyzer of Roche Diagnostics
The aim of this study was to perform a method comparison of three FLC assays that are currently available for routine diagnostics on the Roche Cobas automated platforms

Summary

Introduction

Monoclonal gammopathies are characterized by clonal proliferation of plasma cells leading to the production of monoclonal immunoglobulins, the so-called M-proteins. Plasma cells secrete free light kappa (κ) or lambda (λ) which circulate unbound to the immunoglobulin heavy chains. In plasma cell proliferative disorders, there is often excess production of one of the light chains, leading to an abnormal free light chain (FLC) ratio (κ/λ). About 90% of the newly diagnosed multiple myeloma (MM) patients have an abnormal FLC-ratio and 70% of patients with smoldering multiple myeloma [1]. Because it was shown that 80% of patients with an involved/uninvolved FLC-ratio >100 progresses to MM within 2 years, the International Myeloma Working Group defined that FLC-ratio as a myeloma defining event [1]

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