Development of a rapid and quantitative lateral flow assay for the simultaneous measurement of serum κ and λ immunoglobulin free light chains (FLC): inception of a new near-patient FLC screening tool

Background: Serum free light chains (FLC) are sensitive biomarkers used for the diagnosis and management of plasma cell dyscrasias, such as multiple myeloma (MM), and are central to clinical screening algorithms and therapy response criteria. We have developed a portable, near-patient, lateral-flow test (Seralite (R)) that quantitates serum FLC in 10 min, and is designed to eliminate sample processing delays and accelerate decision-making in the clinic. Methods: Assay interference, imprecision, lot-to-lot variability, linearity, and the utility of a competitive-inhibition design for the elimination of antigen-excess ('hook effect') were assessed. Reference ranges were calculated from 91 healthy donor sera. Preliminary clinical validation was conducted by retrospective analysis of sera from 329 patients. Quantitative and diagnostic results were compared to Freelite (R). Results: Seralite (R) gave a broad competitive-inhibition calibration curve from below 2.5 mg/L to above 200 mg/L, provided good assay linearity (between 1.6 and 208.7 mg/L for kappa FLC and between 3.5 and 249.7 mg/L for lambda FLC) and sensitivity (1.4 mg/L for kappa FLC and 1.7 mg/L for lambda FLC), and eliminated anomalous results from antigen-excess. Seralite (R) gave good diagnostic concordance with Freelite (R) (Roche Hitachi Cobas C501) identifying an abnormal FLC ratio and FLC difference in 209 patients with newly diagnosed MM and differentiating these patients from normal healthy donors with polyclonal FLC. Conclusions: Seralite (R) sensitively quantitates FLC and rapidly identifies clinical conditions where FLC are abnormal, including MM.