Decoding the interference: How therapeutic monoclonal antibodies challenge serum protein electrophoresis and...

Serum protein electrophoresis and immunofixation electrophoresis are routinely used to diagnose and monitor monoclonal gammopathies. However, several therapeutic monoclonal antibodies are detectable by these techniques and may mimic a pathological monoclonal protein, leading to diagnostic confusion. This study aimed to evaluate potential interferences caused by these treatments and to characterize their electrophoretic migration profiles and detection thresholds.

Seven therapeutic monoclonal antibodies (daratumumab, isatuximab, rituximab, elranatamab, teclistamab, eculizumab, and ravulizumab) were assessed using an overloaded hypogammaglobulinemic serum model. Each antibody was tested at seven decreasing concentrations, from one point five grams per liter to zero point one gram per liter. All dilutions were analyzed by capillary electrophoresis and immunofixation electrophoresis.

Validation was performed using daratumumab, for which interference is well documented. Rituximab and elranatamab consistently generated a discrete peak in the slow-gamma region on serum protein electrophoresis, associated with an IgG kappa band on immunofixation electrophoresis. Teclistamab migrated in the mid-gamma region and produced an IgG lambda band, detectable down to zero point fifteen gram per liter on serum protein electrophoresis and zero point zero two gram per liter on immunofixation electrophoresis. Ravulizumab, an IgG kappa antibody migrating in the beta-two region, remained detectable down to zero point five gram per liter and zero point one gram per liter, respectively.

This work specifies the electrophoretic behavior of several monoclonal antibody therapies, helping distinguish therapy-related peaks from true monoclonal gammopathy. These findings support the systematic use of confirmatory strategies-particularly reflex immunofixation-to ensure accurate interpretation of electrophoresis results in patients receiving monoclonal antibody treatment.