Validation of a rapid lateral-flow test for the diagnosis and monitoring of immunoglobulin free light chains: Retrospective analysis of sera from patients with plasma cell dyscrasias

Background: Quantitation of serum κ and λ immunoglobulin free light chains (FLC) is central to the diagnosis and monitoring of patients with plasma cell dyscrasias, including multiple myeloma. At present, laboratory FLC tests offer the only means of quantitating FLC in urine and blood and often have a slow turnaround time that prevents early myeloma diagnosis or identification of relapse. We have developed a rapid lateral-flow test (Seralite™) that simultaneously quantitates kappa and lambda FLCs in blood or urine in 10 minutes using highly-specific anti-κ and anti-λ FLC monoclonal antibodies (Campbell et al., 2013 JIM). Methods: Seralite™ validation was conducted by retrospective analysis of sera from patients with plasma cell dyscrasias from MRC UK Myeloma IX and XI trials. Specifically, 1,975 (MIX n=1,231, MXI n=744) samples at trial entry were used to assess the utility of Seralite™ for diagnosis. Results: Seralite™ displayed excellent clinical concordance with Freelite™ and immunofixation electrophoresis for identification of abnormal FLC levels. Additionally, cohorts of samples from patients with light chain only myeloma, nonsecretory myeloma, and intact immunoglobulin myeloma (IgAκ/λ, IgGκ/λ, IgMκ/λ, IgDκ/λ) were assessed through diagnosis, response to therapy, plateau and relapse. Seralite had excellent concordance with Freelite™ for the quantitation of serum FLC from diagnosis through monitoring. Conclusion: Prospective use of Seralite™ to diagnose and monitor plasma cell dyscrasias at the point-of-care should now be investigated.