Therapeutic Monoclonal Antibody Interference in Monoclonal Gammopathy Monitoring: a Denosumab Experience

A 73-year-old woman was diagnosed with a lambda light chain myeloma. A follow-up immunofixation electrophoresis showed a monoclonal immunoglobulin (Ig)G kappa in addition to the regular lambda band. A monoclonal antibody therapy interference was suspected but her VRD (bortezomib, lenalidomide, dexamethasone) regimen did not include such a medication. Later it was learned that she was prescribed denosumab, a monoclonal human antibody agent to treat bone lesions. The IgG kappa band disappeared 7 months after the first and 4 months after the last dose of denosumab, confirming a case of interference. This case once again emphasizes the importance of delta check and close communication between clinicians to avoid a false result in electrophoresis. It also describes the migration pattern of denosumab. As therapeutic antibodies gain approval and enter into common clinical practice, drug interference will complicate electrophoresis testing in diagnosis and patient follow-up.