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Influence of Immunoglobulin Light Chain Dimers on the Results of the Quantitative Nephelometric Assay by Chang Li, Honglian Geng, Zaixing Yang, Renqian Zhong

Background: Some polymeric forms of immunoglobulin free light chains (FLCs) have been identified, such as dimer, trimer and tetramer, and the quantitative nephelometric assay of κ and λ light chains is very important to the diagnosis and management of multiple myeloma (MM), primary systemic amyloidosis (AL), etc. But, whether polymeric molecules could affect the results of the nephelometric assay, is rarely reported.
Methods: 12 urinary samples from patients with light-chain MM were separated by sodium dodecylsulfate–polyacrylamide gel electrophoresis (SDS-PAGE) and every sample was run with reduced and nonreduced sample buffer in one gel. Urinary κ and λ light chains were measured on the BNII nephelometer. We then added 3 μL β-mercaptoethanol (2-ME) to the samples to transform the dimers into monomeric forms and measured them again.
Results: 10 samples showed obvious dimers by SDS-PAGE, of which 2 samples were κ light chain dimers. Six samples had decreased quantitative results contrasted with the former values. The two samples of κ light chain dimers decreased more obviously.
Conclusions: The light chain dimer combined with more antibodies than the monomer and a larger antigen-antibody complex was formed. The larger complex could magnify the reaction between antigen and antibody of the nephelometric assay and therefore false elevated results could measured.

DOI: Clin. Lab. 2011;57:53-57