B-341 Comparative Study of Free Light Chains in the Framework of the Project Prevalence of Monoclonal Gammopathies in Adult Uruguayan Population

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Abstract Background Within the framework of a study to evaluate the Prevalence of Monoclonal Gammopathies in the Adult population of Uruguay through detection monoclonal bands by capillary electrophoresis and free light chains in serum, the aim is evaluating the comparison of quantification of FLC (Free Light Chains) in this group of patients with 2 assays: Freelite Biding Site® versus Sebia® FLC Elisa. Methods Study period: September 2021 to November 2022. Prospective, single-cohort, descriptive study. Approved by the Hospital de Clinicas Ethics committee, Montevideo, Uruguay.A total of 3905 patients were included (≥40 years, without previously known plasma cell disorder).Serum samples were collected from three health centers, and processed in Clinical Chemistry Laboratory at Hospital de Clinicas, following an algorithm designed to perform electrophoretic proteinogram (by capillary electrophoresis); suspicious samples with monoclonal bands were confirmed by immunotyping, and in some cases by immunofixation (difficult interpretation), and quantification FLC by 2 different assays (Sebia FLC: manual sandwich ELISA technique- BIO-TEK wash/reader; Freelite The Binding Site immunoturbidimetric assay : Spa Plus and Optilite instruments. Comparative analysis of FLC is a transversal and descriptive study.For statistical analysis: Spearman test, Passing and Bablok and Bland-Altman plot. Results κFLC, λFLC and ratio κ/ λ were measured in 93 of the 104 positive serum samples for Monoclonal Gammopathies (new diagnoses, prevalence 2.7%), using two groups Sebia FLC and Spa Plus Freelite, and Sebia FLC and Optilite Freelite. During the project, the Spa Plus (n=48) FLC was replaced with Optilite (n=45), since the comparative group was not analytically homogeneous, so the comparison was carried out in two groups. Spearman rank correlation coefficients between first group (N:48) for κFLC, λFLC and ratio κ/ λ were r=0.596, 0,549, 0.709, respectively (p<0.0001); for the second group (N:45) Spearman rank correlation coefficients were r=0.778, 0.714, 0.878, respectively (p<0.0001). The first group showed good Spearman rank correlation for ratio, although less better correlation for kappa and lambda isolated. Bland Altman showed high media differences in assays for values for Sebia. For the second group, there was a better Spearman Correlation for ratio and in kappa and lambda isolated too. Bland-Altman plot revealed, in the second group analysis, that Freelite provides higher values than Sebia in Kappa and ratio, but not in Lambda. Passing Bablock showed differences systematic and proportional in different group of comparatives. Conclusions There is a good agreement; despite this, within high FLC concentrations, there are particularly significant differences between both assays, in both groups. We found in same cases FLC quantifications with Freelite ratios lower than those reported by the Elisa Sebia assay, which in these patients could change the diagnosis and therefore the opportunity for treatment or the time between follow-ups. In other cases, greater amount of ratio FLC assayed by Freelite, which may represent loss of linearity in subsequent dilutions. Falsely high results may occur due to polymerization of light chains.Our results suggest that Sebia FLC is a valid assay alternative, but needs more studies to demonstrate these findings; the prospective follow up of this group promises more.