Comparison of Serum Immunoglobulin Free Light Chains Assay and Serum Immunofixation Electrophoresis in Patient Transplanted for Multiple Myeloma

Introduction: Serum immunofixation electrophoresis (sIFE) and serum free light chains (sFLC) immunoassays are fundamental for serum monoclonal protein diagnosis and monitoring. In this study, we compared the ability of these assays to detect monoclonal proteins in stem cell transplanted patients. Methods: Three hundred sixty sera belonging to 145 patients affected by MM after autologous stem cell transplantation [113 intact immunoglobulin multiple myeloma (IIMM) and 32 free light chains multiple myeloma (LCMM)] were analyzed by both sIFE and sFLC assay, respectively performed with the Binding Site Minifix Kit and the Binding Site Freelite kit on Cobas-Integra 400 Plus (Roche). Results: Two hundred one samples (55.8%) had an abnormal κ/λ ratio and 32.7% had a monoclonal restricted band in sIFE. For 61.38% samples, there was a concordance between sIFE and sFLC and there wasn't for 139 samples (p<0.0001). Kappa Cohen's coefficient was weak (κ= 0.25). When compared to sFLC immunoassay for IIMM, sIFE demonstrated a weak sensitivity of 80.7%, which increases to 94.74% when we compared only LCMM results. Accuracy of sIFE respect to sFLC was the better for IIMM (70.7%), than for all type MM (61.4%), and there was a significant difference between the accuracy of either of these techniques, when performed singly for all MM type, IIMM and LCMM. Conclusion: sFLC assay role in IIMM monitoring is to be confirmed by further studies. sFLC assay is a sensitive tool for the monitoring of patients after transplantation, and that it may be associated to sIFE assay to better individualizing minimal residual disease.