Characterization of Casirivimab Plus Imdevimab, Sotrovimab, and Bamlanivimab Plus Etesevimab-Derived Interference in Serum Protein Electrophoresis and Immunofixation Electrophoresis.

Imdevimab can be added to the growing list of therapeutic monoclonal antibodies that produce sustained interference in SPEP/IFE. Although casirivimab and sotrovimab also produce assay interference in vitro, these antibodies are not reliably detected in serum from recently infused patients. The value of relative band position in recognizing bands that may represent therapeutic monoclonal antibodies is also emphasized. Clinicians and laboratorians should consider therapeutic monoclonal antibody interference in diagnostic SPEP/IFE and review a patient's medication list when new or transient monoclonal bands are identified.