Detection of Monoclonal Proteins in Sera by Capillary Zone Electrophoresis and Free Light Chain Measurements

Capillary zone electrophoresis (CZE) is increasingly used in clinical laboratories for serum protein separation. The technique is a sensitive method for the detection of monoclonal (M) proteins. However, when compared with immunofixation, CZE fails to detect M proteins in 5% of samples (1)(2). These so-called “false-negative” results encompass low-concentration and “hidden” M proteins (e.g., in the transferrin peak). The goal of this study was to evaluate whether an assay for the detection of free light chains (FLCs) that has recently become available (Freelite®; The Binding Site) can detect the M proteins present in samples that produce false-negative results in CZE. The Freelite assay is a sensitive automated immunoassay for κ and λ FLCs in serum (3) and has been useful for the diagnosis and monitoring of patients with nonsecretory myeloma (4). Moreover, it has been reported that the quantification of FLCs in serum by nephelometry correlates with changes in urinary FLC excretion (5).