Comparison of Hevylite™ IgA and IgG assay with conventional techniques for the diagnosis and follow-up of plasma cell dyscrasia

Background: Heavy/light chain assay allows the characterization and quantification of immunoglobulin light chains bound to heavy chains for each Ig’k and Ig’ immunoglobulin class, discriminating between the involved/uninvolved isotypes in plasma cell dyscrasia. The Ig’k/Ig’ ratio (heavy/light chain ratio) enables to monitor the trend of monoclonal component during therapy and disease evolution. Objective: In this study, we evaluate the impact of the heavy/light chain assay in monitoring multiple myeloma patients in comparison with conventional techniques. Methods: Serum samples of 28 patients with IgG or IgA monoclonal component were collected for a mean of 109 days and analyzed. The heavy/light chain assay was compared with classical immunoglobulin quantification (Ig’Tot), serum immunofixation electrophoresis, serum protein electrophoresis, and serum-free light chains quantification. Serum samples from 30 healthy patients were used as control (polyclonal). Results: Heavy/light chain ratio and serum immunofixation electrophoresis were comparable in 86% of the cases, and free light chain ratio and heavy/light chain ratio in 71.8%. Heavy/light chain assay and Ig’Tot measurements showed a concentration-dependent agreement in monoclonal patients. The heavy/light chain assay was able to quantify the monoclonal component migrating in SPE b region: this occurred in 10% of our IgG and 50% of our IgA patients. Conclusions: The concordance scores indicate that heavy/light chain and Ig’Tot assays show differences at high monoclonal component values. The heavy/light chain ratio, serum immunofixation electrophoresis, and free light chain ratio showed partial concordance. Our study confirmed that, in the context of heavy/light chain assay, heavy/light chain Ig’k and Ig’ absolute values and heavy/light chain ratio are both important tools to monitor the presence of monoclonal component that are difficult to be identified in SPE.