Characterization of the Migration Profile of 36 Therapeutic Monoclonal Antibodies in Serum Protein Electrophoresis and Immunofixation.
BACKGROUND Therapeutic monoclonal antibodies (t-mAbs) are widely used in oncology, hematology, and immune-mediated diseases. Some t-mAbs are detectable by serum protein electrophoresis (SPEP) and immunofixation (IF), potentially mimicking monoclonal gammopathies. Despite widespread use, migration profiles of many t-mAbs remain incompletely described. METHODS Thirty-six t-mAbs were tested using Sebia Capillarys 3 (SPEP) and Hydrasis (IF) systems. Normal human sera, free of electrophoretic abnormalities, were spiked with each t-mAb at its reported maximum therapeutic concentration (Cmax). Electropherogram data were processed with a Python-based workflow for axis alignment, standardized profile overlay, and visualization. T-mAbs not detected at Cmax were assessed at 500 mg/L to determine their electrophoretic migration profiles. RESULTS No interference was observed below 110 mg/L. All t-mAbs tested above this threshold were detectable by SPEP and IF. Migration patterns were newly characterized for several t-mAbs, including bispecific and drug-conjugated antibodies, and confirmed for previously described agents. Overlay analysis enabled refined attribution of migration zones within alpha and beta regions. T-mAbs detectability was summarized in a consolidated table. A stepwise decision algorithm was developed to guide interpretation of suspected t-mAb-related interference. CONCLUSION This study expands knowledge of t-mAb interference with SPEP and IF and provides standardized electrophoretic profiles for established and emerging therapies. The summary table and decision algorithm offer practical tools for clinical laboratories, facilitating interpretation of electrophoretic patterns, supporting differentiation between t-mAb and monoclonal gammopathies, and highlighting the need for continued characterization of novel t-mAbs entering routine practice.