Comparative analysis of three different serum-free light chain assays in the diagnosis of multiple myeloma

BACKGROUND: The lack of analysis methods and standardization are the core problems of serum free light chain (sFLC) detection in Multiple myeloma (MM). This study validated a new KHB sFLC assay through comparative analysis with conventional assays. MATERIALS AND METHODS: Serum samples from 97 hospitalized MM patients were continuously collected. KHB, Freelite and N Latex assays were used to detect sFLC. The Bland-Altman and Passing-Bablok regressions were used for methodological comparison and bias evaluation. Spearman's test and Cohen's kappa coefficients were used to evaluate the correlation and clinical concordance. RESULTS: The sFLC results for KHB, Freelite, and N Latex showed a significant correlation. Passing-Bablok regression analysis revealed strong concordance between the KHB and N Latex for κFLC, and between KHB and Freelite assays for λFLC and FLC-ratio (κ/λ). When using N Latex and Freelite assays for sFLC determination, selecting iFLC/niFLC ≥ 20 or iFLC/niFLC ≥ 100 could lead to different clinical treatment decisions for approximately 9%∼12% of patients. When using KHB and Freelite assays for sFLC determination, selecting iFLC/niFLC ≥ 20 or iFLC/niFLC ≥ 100 could lead to different clinical treatment decisions for approximately 5%∼7% of patients. CONCLUSION: KHB, as a sFLC detection method based on polyclonal antibodies and immunoturbidimetric principles, has a good correlation between its detection results and freelite and N Latex. The absolute difference in sFLC results among the three assays increased with increasing sFLC concentration, and selecting the same cutoff value for iFLC/niFLC may lead to inconsistent clinical treatment decisions in some patients.