M-protein detection using two immunofixation electrophoresis systems and impact of daratumumab interference on disease monitoring.

M-protein identification by immunofixation electrophoresis (IFE) varies depending on equipment and reagents used. Daratumumab (DARA), an IgGκ monoclonal antibody for multiple myeloma treatment, frequently interferes with IFE interpretation. This study compared the analytical performance of two IFE systems and evaluated the impact of DARA interference on IFE interpretation. We compared the current system, Epalyzer 2 Jr. (Helena), with the target system, HYDRASYS 2 (Sebia), using 104 clinical samples including suspicious positive cases, 20 AL amyloidosis patients, and 76 other clinical cases from our hospital. For 10 DARA-treated samples, changes were evaluated before and after DARA displacement using the HYDRASHIFT Daratumumab (Sebia) assay. The concordance rate between the two systems ranged from 60.0% to 88.5%. AL amyloidosis patient samples showed the lowest agreement rate. In 20 discordant cases, HYDRASYS detected additional bands, mainly light chains, that were missed by Epalyzer. Among DARA-treated samples, concordance was observed in only one case. In the remaining nine cases, IgGκ bands detected by the current method disappeared following DARA displacement, with three cases becoming entirely negative. HYDRASYS demonstrated superior sensitivity for detecting M-proteins and free light chains compared to Epalyzer. When DARA-derived bands interfere with IFE interpretation, DARA displacement is necessary for accurate assessment of hematologic response in patients with multiple myeloma.