Direct Measurement of Serum Immunoglobulin Heavy and Light Chain Pairs for Identification of Monoclonal Gammopathy and a Performance Comparison with Capillary Electrophoresis

ABSTRACT

BACKGROUND: Determination of monoclonal gammopathy through conventional protein electrophoresis is sometimes difficult because of the presence of large proteins such as haptoglobin and transferrin, which may obscure the results. Ambiguity in an electrophoresis band can give rise to confusion or difficulty in interpretation. The heavy chain/light chain assay (HLC assay) using Hevylite antibody (The Binding Site, UK) has recently been developed for the accurate measurement of monoclonal proteins. We compared the immunotyping (IT) profiles to the immunoglobulin (Ig) heavy/light chain measurements obtained using the HLC assay and observed the ratios between intact Ig kappa and lambda. METHODS: We collected 35 and 28 sera from patients with suspicious and definitive monoclonal protein, respectively. Then we performed serum protein electrophoresis (SPEP) and IT by Capillarys2 (Sebia, USA). Monoclonal protein production was investigated using Freelite antibody (The Binding Site) and specific Ig(G, A)kappa and Ig(G, A)lambda Hevylite antibodies. The results were analyzed using PASW 18.0 for Windows (IBM, USA). RESULTS: Direct measurement of Ig heavy/light chains showed discordant IT results for 12 (34.2%) of 35 patients' sera with suspicious SPEP pattern and identical IT results for 28 patients' sera with definitive monoclonal peak in the SPEP results. Overall, the results of the HLC assay and IT showed good agreement (kappa=0.718, P=0.000 by cross-tabulation Gamma, Kappa analysis). CONCLUSIONS: The results of direct measurement of serum Ig heavy chain/light chain pairs were comparable to those of IT and were helpful for determination of monoclonality in the case of ambiguous electrophoresis results. Measurement of the heavy chain/light chain pair ratio also allowed precise quantification of the monoclonal Igs with ambiguous electrophoresis patterns and identification or discrimination of clonality.