Performance and comparison of FLCCheck: a novel serum free light chain assay for the Auxiliary Diagnosis of Multiple Myeloma

Abstract

Background: Multiple myeloma (MM) is a malignant bone marrow disorder characterized by the abnormal proliferation of plasma cells. The measurement of serum free light chains (FLC) is a standard diagnostic and management tool for MM. The International Myeloma Working Group utilizes the iFLC/uFLC ratio to distinguish smoldering multiple myeloma (SMM) from active MM requiring therapeutic intervention.

Objectives: We employed a novel serum free light chain (FLC) assay kit, FLCCheck, to evaluate its consistency with established traditional methods.

Design and methods: We collected 115 samples from 72 patients and tested them using FLCCheck, Freelite, and N Latex FLC. The data obtained from each method were analyzed using Passing-Bablok and Bland-Altman methods, and a chi-square analysis was performed to assess the consistency between the tests. Finally, we used the three methods to calculate and analyze the κ/λ ratio for two patients during their clinical treatment.

Results: The FLCCheck assay demonstrated a validated linear range, high precision, and strong resistance to interference for both κ and λ light chain detection. By incorporating blocking peptides to reduce cross-reactivity, we improved the reliability of the diluted recovery by more than twofold. The results indicate that FLCCheck exhibits the highest correlation with N Latex FLC, particularly regarding the κ/λ ratio and κ FLC. We also monitored the therapeutic efficacy in MM patients, the results indicated that the three methods followed comparable trends; yet, FLCCheck distinguished itself by demonstrating a more rapid response with the highest amplitude variation.

Conclusions: Our findings show satisfactory consistency between the three FLC testing methods, but their interchangeability is not recommended. Consistent use of the same assay method across all reports is essential. The development of new FLC detection methods is valuable for optimizing disease monitoring, prognosis, and the management of multiple myeloma and related diseases.

Keywords: FLCCheck; Multiple myeloma; Serum free light chain; Turbidimetric immunoassay.

Fig. 1

Comparison of N Latex FLC with Freelite in the determination of FLC. Passing-Bablok (A) and Bland–Altman (B) analyses were conducted using 115 serum samples obtained from patients diagnosed with newly identified or relapsed multiple myeloma, Waldenström’s macroglobulinemia, plasma cell leukemia, elevated immunoglobulin levels, leukemia, and lymphoplasmacytic lymphoma. The results for the determination of κ and λ FLC and the κ/λ ratio, as measured by N Latex FLC and Freelite assays, are presented. Bland–Altman plots demonstrate a concordance between N Latex FLC and Freelite measurements. A positive bias indicates higher values for the determination of FLC by Freelite compared with N Latex FLC

Fig. 2

Comparison of N Latex FLC with FLCCheck in the determination of FLC. The results of the Passing–Bablok analysis (A) and the Bland–Altman analysis (B) are presented. Bland–Altman plots demonstrate a concordance between N Latex FLC and FLCCheck measurements. A positive bias indicates higher values for the determination of FLC by FLCCheck compared with N Latex FLC

Fig. 3

Comparison of Freelite with FLCCheck in the determination of FLC. The results of the Passing–Bablok analysis (A) and the Bland–Altman analysis (B) are presented. Bland–Altman plots demonstrate a concordance between Freelite and FLCCheck measurements. A positive bias indicates higher values for the determination of FLC by FLCCheck compared with Freelite

Fig. 4

Discrepancies of κ/λ ratio values in the clinical course of treatment. A and B refer to Patient 1 and Patient 2. The κ/λ ratios were measured using Freelite, N Latex FLC, and FLCCheck during the clinical course of patients at the indicated time points (tp)