Evaluation of the N Latex FLC free light chain assay on the Siemens BN analyser: precision, agreement, linearity and variation between reagent lots

Abstract

Background: The clinical utility of serum k and l free light chains (FLC) for the diagnosis and prognosis of plasma cell proliferative disorders is well established. We assessed the analytical performance of the N Latex FLC assays and compared it with the Freelite TM assays.

Evaluation of the N Latex free light chain assay in the diagnosis and monitoring of AL amyloidosis

“…Differences between the two assays may also reflect the subject group evaluated, e.g., AL group versus a more heterogeneous hospital population [14] (Table 3) or the FLC concentration. This demonstrates the importance of performing analytic validation studies in different light chain disease populations rather than just in general hospital or normal donor populations.…”

“…While this tendency was less marked for the Lambda FLC comparison, the uninvolved Lambda FLC concentrations generally were lower by Freelite TM compared to the N Latex FLC assay (Figure 4). Table 3 summarises the Passing-Bablok regression slope for the κ and λ assays in this study of AL amyloidosis compared to a more general hospital population [14]. In AL amyloidosis where the measured FLC corresponded to that involved by the AL disease process the slope is significantly lower compared to the uninvolved FLC as the 95% confidence intervals do not overlap.…”

“…This new FLC assay appears to have some analytical advantages over the Freelite ™ assay [14] but lacks clinical validation, particularly in AL amyloidosis where FLC measurement has such a central and critical role in patient management. We assessed the utility of the N Latex FLC assays in the diagnosis and monitoring of AL amyloidosis and compared it with the polyclonal Freelite ™ κ and λ FLC assays.…”

Response to Basu et al

“…We welcome the critique of our paper 1 by Basu et al 2 The analytical challenges of free light chain (FLC) assays are well documented 3,4 and need to be considered when evaluating an alternative method. The precision study was performed at the correct sample dilution as recommended by the manufacturers.…”

“…The recommendation that we should repeat discordant results at different dilutions is interesting and we refer the authors to Table 1. 1 The requirement that a new assay must be validated de novo in clinical studies before use needs to be carefully considered. Both the Freelite and N Latex assays are approved for clinical use by the relevant regulatory authorities and furthermore the guidelines do not appoint an exclusive manufacturer.…”