A Comparative Analysis of Freelite and N Latex FLC Assay for the sFLC Measurements in Suspected Patients of Monoclonal Gammopathy

With the introduction of newer platforms for sFLC estimation, more comparative attempts are required to establish an assay-specific reference range, that can be used in the day-to-day clinical management of the patients, as the revised criteria for the diagnosis of myeloma recommend the use of involved Free light chain (FLC)/uninvolved FLC ratio as myeloma defining event, solely relying on Freelite assay. This was an observational study that included 101 patients, 55 (54.5%) with M-protein (myeloma), and 46 (45.5%) without M-protein. The estimation of the sFLC assay was carried out at two separate platforms, the Freelite Assay (The binding Site, Birmingham, UK) on a Siemens BNII Nephelometer, and the N Latex FLC reagent on Atellica NEPH 630 (Siemens Healthineers, Eschborn, Germany). The comparative correlational analysis of the two assays for estimation of kappa-, lambda FLC, and kappa/lambda ratio showed a strong to a very strong association (P-value < 0.005) among total patients, however, this was reduced to weak to moderate association among patients with M-protein (P-value < 0.005). The contingency analyses to evaluate the agreement between the assays also showed a similar trend. A better concordance for the kappa/lambda ratio between the two assays was achieved while expanding this ratio. Our study concluded that two assays showed a better agreement among the patients without M-protein, but these two cannot be used interchangeably for the clinical management of myeloma patients.